The answer is that it decreases your net density. The person has a density of 998 Kg/m3. The parachute has a mass of 7Kg so that increases the Kg by 7 and the m3 by 0.2*0.3*0.3 = 0.05 cubed
New density =1006Kg per 1.07 m3 = 958.09 Kg per meters cubed.
Next we add the air in the parachute at 1.225 Kg/meters cubed
The volume =1/2 x 4/3 pi r cubed approximately as it is parabolic actually
d=11 ft = 3.3528 m = r=1.6764 m
volume = 39.4685 m cubed
So the mass has gone up by 48 Kg and the volume has gone up by 39.4685 m cubed
So we arrive at 1045.04685 Kg per 40.5385 m cubed = 25,77 Kg/m3
So the parachute changes your net density from 998 Kg/m3 to 25,77 Kg/m3
This is compared to air at 1.225 Kg /m cubed at sea level or 0.018 Kg/m3 at 30,000 ft
The terminal velocity is determined from the ratio of the instantaneous density of the air and the net density of 25.77 Kg/m3 X the ratio of the viscosity of the person wearing a parachute/the air. The viscosity also has to be multiplied by a variable related to the Renolds Number to scale it up.
The answer then, without the parachute 125 mph
with it 25.77/1.225 x 9.7126415 E-5/1.81206E-5 = 5.36 m/s
5.36 m/s = 12 mph assuming laminar flow and Renolds no =1
When we are in water we are at our Natural density layer surrounded by a medium very similar to our density. Some people float on the water. Float meaning having the same natural density as the surface of water. Others are more dense and are stable 5m below the surface of the water. We are at this natural density as our origins were where we once lived, in the sea. So our density is very similar to sea water that has slightly higher density than pure water.
Once at our natural density level we feel no pull. So unless an object is not in it's natural layer it will not feel any gravity force. This gravity force is just the sorting force applied by the net inertia applied towards the centre of the Earth brought on by the differences of the inertia at the side of the Earth being further away from the sun and nearer to it as the Earth rotates. This creates a squashing inertia from the just over half of the world and a pulling inertia from the side nearest the sun. The plane that is the same as the Earths inertia, is an 3D arc shape of equal distance to the sun, this passes through the centre of the Earth. The net greater squashing inertia than the pulling inertia creates a net inwards inertia and as the Earth rotates on a tilted axis, this inertia is then directed at the centre of the Earth. The inertia is only converted into a force when there is a difference in density between materials. Imaging a pile of competing molecules all lined up with the centre of the Earth and free to move. The densest molecules will always have a positive density and a force will be created to move it around the next molecule until after many handshakes it finally reaches the centre of the Earth. All this turmoil has long sinced stabilised and only materials placed out of their natural density level by man usually are subject to a sorting force. If the material is blocked from moving freely by a more dense material in the way it carries on feeling the sorting force.
When it rains many tonnes of rain are dropped but soon it seeps down through the less dense earth then through the gaps in the rocks to underground streams that eventually reach rivers and finally the rain gets back to the rains natural density level, the sea.
We are drawn to go to the sea side for the same reason