3(3x + 5) = 4x What is x?

On the left side of the equation, use the distributive property: 3(3x + 5)  =  3(3x) + 3(5)  =  9x + 15:

9x + 15  =  4x                    Get all the x-terms to one side by subtracting 9x from both sides:

9x - 9x + 15  =  4x - 9x

    15  =  -5x                       Divide both sides by -5:

    15 / -5  =  -5x / -5

    -3  =  x