Leave the first polynomial untouched. Now distributive the negative sign (the subtraction sign) to the second polynomial. This means you would now get 8y^2 + y - 5. Now here are the two polynomials: 2y^2 + q + 8y^2 + y - 5. Now split it so you can combine like terms, like this: (2y^2 + 8y^2) + (q) + (y) - 5. You final result should be 10y^2 + q + y - 5.
Hope this helped. If you need help I can explain further. Just tell me what you don't understand.