HELP PLEASE NEED ASAP- FIVE QUESTIONS ON SCIENTIFIC NOTATION

Combine the like terms in the expression.

A. -12x^4 + 7x^4 + 6x^4

B. 2r + 7r + 16x

C. 30z^8 + 7z^8 + 8z

D. 15a^2 - 15b^2 + 13a^2 - b^2

E. 7x^2 - 82x + 12x^2 - 2x