A wire of cross section A is stretched horizontally between two clamps located 2l length apart. A Weight W kg is suspended from the midpoint of the wire. If the mid-point of the wire sags vertically through a distance x, find the strain produced. Note $x<l$.
By the great Hadron Collider, add a drawing at least! Respect hard earned knowledge. Or you will keep getting down votes.
The mass W produces a total force of W*9.8 Newtons downwrds and this force is shared by two "arms" of the sagging wire so we divide it by 2. Now the wire pulls the weight at some angle so it must pull with a higher force F to balance the force downwards. So we divide by the sine of that angle and find the force F.
By "strain" I assume you mean tension so you divide the force F on the wire by the thickness A of the wire and it's done.