Question

Subtract (2x3 + 9x − 8) − (4x2 − 15x + 7).

Answer 1

2x^3 + 9x - 8 - (4x^2 - 15x + 7)....distribute thru the parenthesis
2x^3 + 9x - 8 - 4x^2 + 15x - 7....combine like terms
2x^3 - 4x^2 + 24x - 15 <==

Answer 2

Distribute invisible -1

-1(4x^2-15x+7)=-4x^2+15x-7

now we have
2x^3+9x-4x^2+15x-7
group like terms

2x^3-4x^2+9x+15x-8-7
add
2x^3-4x^2+24x-15