SOLUTION: A 6100 kg rocket is set for vertical firing. If the exhaust speed is 1300 m/s, at what rate (in kilograms/second) must the gas be ejected to supply the thrust needed to give the ro

To give the rocket an initial upward acceleration of 24.0 m/s^2, the force

 = ma = 6100 kg * 24 m/s^2   (Newton's second law)

must be applied. (The lower index  stands for rocket).

This force is produced by the exhausting (ejecting) gases in accordance with the formula

 = r*v = r kg/s * 1300 m/s

where "v"  is the gases ejecting speed, "r" is the mass rate of the gases and the lower index  stands for gases.

So, your equation is   = ,  or, which is the same, 

6100*24 = r*1300.

Solve it for the unknown "r" and get the answer.