Relations and Function - finding gof and fog

Ok got this cleared,

Here is the detailed solution for the question.

When we compute for gof, the range of f is the domain of g. So on computing f first, we end up with the values \left\{ 3,5,7 \right\} which on proceeding further leads to \left\{7,9,10 \right\}

So we finally have gof as \left\{(1,7),(2,9),(3,10) \right\}

But when we take g first for fog, range of g must be \left\{ 1,2,3 \right\} which is not the case here. Thus, its not defined

EDIT: Didn't see your post Anirudh. Yes, the reason is correct. Thanks