subtract.
(5x^6+9x^4-2x^3-3)-(8x^6=8x^5+x^4-5)
Your = sign before 8x^5 should be + or -.
All you have to do is combine (add or subract) terms with the same power of x. For example, the constant term will be -3 -(-5) = 2
and
5x^6 -8x^6 = -3x^6
You do the rest.