x/(x - 5) = 4/(x - 4) + 12/(x^2 - 9x + 20)
Note that x^2 - 9x + 20 can be written as (x-5)(x-4), so multiply all terms by (x-5)(x-4) to get
x(x-4) = 4(x-5) + 12, or x^2 -4x = 4x -20 + 12 or x^2 - 8x +8 = 0.
Use the quadratic equation to find the values of x.
