jmc

Combining like terms, we find that $$\begin{array}{rl}& (x^5+3x^2+3x^5)-(x^7+2x^2+6x^5)\\ & =(x^5+3x^5-6x^5)+(3x^2-2x^2)-x^7\\ & =\boxed{-x^7-2x^5+x^2}.\end{array}$$