To solve this equation, we can start by using the property of logarithms that states log a + log b = log(ab).

Therefore, we can rewrite the equation as:

log 25(x^2+6x) = log 25(x^2+126)

By using the property of logarithms, we get:

x^2 + 6x = x^2 + 126

Now, we can simplify the equation by subtracting x^2 from both sides:

6x = 126

Now, divide both sides by 6 to solve for x:

x = 21

Therefore, the solution to the equation is x = 21.