adding polynomials

When adding polynomials you can only add numbers and variables with the same exponents.

For Example: (3a^5-9a^3+4a^2) + (-8a^5+8a^3+2)
3a^5+(-8a^5)-9a^3+8a^3+4a^3+4a^2+2
= -5a^5-a^3+4a^2+2