3x+²+15x+18

Your equation is not complete. It is missing a sign.

If it is

3x^2 - 15x - 18 = 0

3(x+1)(x-6) = 0

x = {-1, +6}

If it is

3x^2 - 15x + 18 = 0

3(x-2)(x-3) = 0

x = {2, 3}

If it is

3x^2 - 15x - 18 = 0

3(x+1)(x-6) = 0

x = {-1, +6}

If it is

3x^2 - 15x + 18 = 0

3(x-2)(x-3) = 0

x = {2, 3}