Perhaps the original post has been changed but I don't see how either of those really helps. If c= 2, then f(c)= f(2)= 4- 4= 0 but the problem said "let e be any number between -1 and 15 and find c such that f(c)= e". Yes, f maps (1, 5) to (-1, 15) which means there is a solution.
storchfire1X, the equation is the same as the quadratic equation . You can use the quadratic formula to solve it. The quadratic formula will give two roots for the equation but only one of them will be between 1 and 5