I need help with this problem:

63n^3+54n^2-105n-90

The answer is: 3(3n^2-5)(7n+6)

I don't understand the answer... when I tried to solve it, this is what I did:

(63n^3+54n^2)-(105n-90)

9n^2(7n+6)-3(35n+30) I am stuck here, I don't know what to do, the numbers in the ( )s are not the same... I don't know what to do next. I don't understand how from here the answer is 3(3n^2-5)(7n+6).

Please help me. Thank you!