The formula to start with is (DC +CE) * CE = (AB + BE) * BE
Replace the letters with the numbers and equations:
(1 + x+4) * x+4 = (11 + x+1) * x+1
(x+5) * (x+4) = (x+12) * (x+1)
x^2 + 9x +20 = x^2 +13x +12
x^2 = x*x = 2x
11x+20 = 15x+12
20 = 4x+12
8 = 4x
x = 8/4
x = 2
