Wow, where are you getting these problems?.
Try starting with parts:
\(\displaystyle \int_{-1}^{0}n(x+e^{x})^{n}dx=\int_{-1}^{0}\frac{x+e^{x}}{1+e^{x}}[(x+e^{x})^{n}]'dx\)
Using parts, we get:
\(\displaystyle \frac{1}{2}-\frac{(-1+e^{-1})^{n+1}}{1+e^{-1}}-\int_{-1}^{0}(x+e^{x})^{n}\left[\frac{2e^{x}-x+1}{e^{2x}+2e^{x}+1}\right]dx\)
Now, can you finish and see what the result is?.