Rocket Question

...

Can we get some more dimensions on that pic...?

Hi !

I seem to get the right answer when I round up, and use g=10 instead of 9.81... but I don't think I am quite correct.
I have shown it doesn't lift off immediately since the weight is greater than the upthrust initially.
I know the time taken should be for the weight to balance the upthrust exactly, I found the difference in weight, divided by g and then divided by the 16 rate. but this would take into account the fuel AND rocket?

so its ok to use that rate along with the total mass of rocket and fuel? since the rocket mass doesn't change?

The rate of change of mass is $\frac{dM_R}{dt}+\frac{dM_F}{dt}=\frac{dM_F}{dt}$ since the mass of the rocket doesn't change. So yes, it's fine to use the given rate of change on its own.