A firework of mass 1 kg is placed on the ground and ignited , the impulse created by the explosion causes it to move vertically upwards with an initial velocity of 50 m/s,after 4 seconds a 2nd explosion takes place in air and the horizontal impulse forces cause it to separate into 4 identical pieces

Question : Find the horizontal velocity imparted on a piece after the 2nd explosion

So i tried applying the conservation of linear momentum , but i cant get an answer , can someone explain how i solve this type of problem ?