OK lets do this very slowly for the very slow people out there.

There are 1000000g in 1tonne.

So if and only if the question said 25.0000000T as the start weight you could put the answer in g.

However given 25T as a start weight the answer should be in T anything else is false precision.

Given:

Take Ar(CaO) to be 56 and Ar(CaCO3) to be 100.

you should use that data not other data your friend has looked up.

Read the question and answer the question that has been set.

If you start with a reaction equation you'd see how wrong your original answer was.