First I'll try to retype your given equations.
Try to plug in u and du/dx into dy/dx
the question is find dy/dx at the indicated value of x
y = sqrt[u^2 +5], where u = (1-x)/(1+x) ; x=-2
the answer the book has is 6/sqrt14 but I am getting 3/sqrt14
here is my work
1/2[u^2 + 5]^(-1/2) * 2u * d/dx(u)
comes down to [1/2] * 14^(-1/2) * (-6) * (-1)
giving me 6/2sqrt14 -> 3/sqrt14
thank you!