algebra
posted by math .
2x/x4 + 4/x3 = 8/x^27x+12

did you notice that
x^2  7x + 12 = (x4)(x3) which happen to be denominators of the first 2 terms?
So the LCD is (x4)(x3)
Multiply each term by that LCD to get
2x(x3) + 4(x4) = 8
2x^2 + 4x  30 = 0
x^2 + 2x  15 = 0
(x+5)(x3) = 0
x = 5 or x = 3
BUT x=3 would make the expression undefined,
so
x = 5