What is the difference of polynomials (8r6s3-9r5s4+-5r6-4r5s4)

If you would like to solve (8r^6s^3 – 9r^5s^4 + 3r^4s^5) – (2r^4s^5 – 5r^3s^6 – 4r^5s^4), you can do this using the following steps:

(8r^6s^3 – 9r^5s^4 + 3r^4s^5) – (2r^4s^5 – 5r^3s^6 – 4r^5s^4) = 8r^6s^3 – 9r^5s^4 + 3r^4s^5 – 2r^4s^5 + 5r^3s^6 + 4r^5s^4 = 8r^6s^3 – 5r^5s^4 + r^4s^5 + 5r^3s^6

The correct result would be 8r^6s^3 – 5r^5s^4 + r^4s^5 + 5r^3s^6.