To solve this equation, we can simplify both sides separately.

On the left side, we have 9x - 4x. This simplifies to 5x.

On the right side, we have 6^17 / 6^15. When dividing with the same base, we subtract the exponents. So, this simplifies to 6^(17-15) = 6^2 = 36.

Now, we have the equation 5x = 36. To solve for x, we divide both sides by 5:

5x/5 = 36/5
x = 7.2