Answer
7
Work Step by Step
For any positive real number $b$ (such that $b\ne1$), we know that $log_{b}b^{r}=r$ (as long as $r\gt0$).
For $log_{2}128$:
We know that $2^{7}=128$, so we can replace 128 with $2^{7}$.
Therefore, $log_{2}128=log_{2}2^{7}=7$.