f(x) = x / (x+ 4) [1,8]

I found fprime(x) to be 4/(x+4)^2

Then I used (f(b) - f(a)) / (b -a) and found that to be 7/15

I set the equation to zero to solve for c and my answer comes out wrong. (squarroot60/7)-4

PS How do I use the math syntax keys on this forum?