Add. (1/4x^4+3/4x^3+7/8x^2+9)+(-3x^4+1/8x^2-9. Please help, this is like chinese to me. Thank you.

Just collect (combine) terms with the same power of x. This leaves you with

-(11/4)x^3 + (3/4)x^3 + x^2

The two constant terms, +9 and -9, cancel each other.