O man i hate derivatives but this looks like you have to use quotent rule.
y/1-e^x= f'(x)g(g)-f(x)g'(gx)/g(x)^2 (derivative of y is just y prime or y' and derivative of e^x is just e^x times derivative of x which is just 1) (for example e^x^2 would just be e^x^2 x 2x)
y'(1-e^x)-y(1-e^x) / (1-e^x)^2 is your answer