1/x + 1/1+x = 7/12 ^ LCM of x, (1 + x), & 12 = 12x(1+ x)
to get rid of the denominator multiply the whole expression by the LCM
Thus
12x(1+x)[1/x + 1/1+x] = 12x(1+x)7/12 = 7x(1 + x)
12(1+x) + 12x = 7x + 7x²
12 + 12x + 12x = 7x +7x²
12 +17x = 7x²
0 = 7x² -17x -12
(7x +4)(x - 3) = 0
x = -4/7 0r x = 3
