To simplify:

First, distribute the negative sign in front of the second expression:

x^2 - 4/5x - 10 - x^2 + 4x + 4/5x + 10

Now, combine like terms:

x^2 - x^2 - 4/5x + 4x + 4/5x - 10 + 10
= 0 + 4x - 10 + 10

This simplifies to:

4x