Subtract (2x^3 + 9x-8) - (4x^2-15x+7)

Distribute the “-“ to the second expression. Once you got that, combine the two expressions so they would be:
2x^3 + 9x -8 - 4x^2 + 15x - 7

Then combine like terms. So you would combine 9x + 15x and -8 -7.

Put it in correct order, largest exponents first.
2x^3 - 4x^2 + 24x -15

There ya go !

Iam not sure but i think the answer is b