To solve this equation, we can start by simplifying both sides of the equation:

X^2 + 6x - 500 = x^2 - 20x + 20

Next, we can rearrange the terms on both sides to collect like terms:

6x + 500 = -20x + 20

Now, we can combine the x terms on one side and the constant terms on the other side:

26x = 520

Finally, we can solve for x by dividing both sides by 26:

x = 520/26
x = 20

Therefore, the solution to the equation is x = 20.