Given :
.
Thrust is : Fthrust = 3.0 * 105 N
.
Weight of rocket (W) = 20,000 kg
.
We know that :
.
F = Fthrust - W
.
or ma = Fthrust - W
.
or m = ( Fthrust - W ) / a
.
= ( 3.0 * 105 - 20,000 ) / a
.
= 280,000 / a -------------(1)
.
If acceleration value is given , then using equation (1) we can find mass value.
.
Please provide acceleration (a) value.
.
Hope this helps u!