Should the question read 6/x + 6/(x+9)=1? If so, we need to get rid of the fractions by multiplying both sides of the equation by x(x+9). This gives us 6(x+9)+6x=x(x+9). Open the brackets: 6x+54+6x=x^2+9x. Gather all the terms together and write in quadratic form: x^2+(9-6-6)x-54=0. That is, x^2-3x-54=0. Applying the formula we get:
x=(3+/-sqrt(9+216))/2.
Sqrt(225) is 15, so this becomes (3+/-15)/2. [+/- means plus-or-minus.] The two roots are 9 (18/2) and -6 (-12/2). We didn't really need the formula because the equation factorises into (x-9)(x+6)=0. These values of x can be put back into the original equation to check the result. 2/3 + 1/3 = 1 and -1 + 2 = 1. Correct!