Dear Aspirant, this is an important question for IIT JEE.The answer is,

Mass of each bullet = 50g = 0.05 kg

velocity = 1000 m/s

let the number of bullets per second = n

Average force acting on gun = 200N

Rate of change of momentum = force

=> nmv = Average force

=> n × 0.05 × 1000 = 200

=> 50n = 200

=> n = 200/50= 4

Bullets per second = 4

bullets per minute = 4× 60 = 240

Thus, 240 bullets per minute were fired.

I hope this helps you!