Find the derivative of $h(r)=(ae^r) / (b + e^r)$. I got this answer 
$$\frac{ae^r(b-1)}{(b + e^r)^2}.$$
But in the solution page, they put the answer 
$$\frac{abe^r}{ (b + e^r)^2}.$$
Which is the correct answer? There answer is correct if $d/dx(b) = 0$, I thought it's $1$.

According to the quotient's rule, the derivative $h'(x)$ should be equal to
$$\frac{(ae^r)'(b+e^r)-(ae^r)(b+e^r)'}{(b+e^r)^2}=\frac{ae^r(b+e^r)-(ae^r)(0+e^r)}{(b+e^r)^2}.$$
Can you take it from here? Did you find your mistake?
