The answer would be =4x^2-6x+b-10 I can show you the steps if you would like
1)Remove all ()
=7x^2-2x+b-(3x^2+4x+10)
2)-(3x^2+4x+10)
3)Distribute ()
=-(3x^2)-(4x)-(10)
4)Group like terms
=7x^2-3x^2-2x-4x+b-10
5)Add like elements
=7x^2-3x^2-6x+b-10
6)Add similar elements again
=4x^2-6x+b-10
7)Answer is
=4x^2-6x+b-10
