Calculate the thrust acting on a rocket

[ASidd]

Homework Statement

A 20,000 kg rocket exhausts gasses at a constant 700 kg/sec at 300 ms^-1
Deduce the thrust applied to the rocket by its engines

Homework Equations

The only equation I know is a= T- mg/m

Where T= thrust
a=acceleration
m=mass

The Attempt at a Solution

I don't know any other formulas and I can't use the one above because I don't have the acceleration
Please help??

 

[HallsofIvy]

Use "conservation of momentum". You can calculate the momentum of the exhaust gases from the information given and that must be equal to the momentum of the rocket itself. What thrust will give that mometum?