For what value of x will (3 + x)/(5 + x) and (1 + x)/(4 + x) be equal?
(3 + x)/(5 + x) = (1 + x)/(4 + x) cross multiply
(x+3)(x+4) = ( x+1)(x+5) expand
x^2 + 7x + 12 = x^2 +6x + 5 simplify
x = - 7
