Answer
$\log_2{128} = 7$
Work Step by Step
Note that $128=2^7$. Thus, the given expression is equivalent to:
$=\log_2{(2^7)}$
RECALL:
For any real number $a \gt 0, a \ne1$, and any integer $n$:
$\log_a{(a^n)} = n$
Use the rule above to obtain:
$\log_2{(2^7)} = 7$
Thus,
$\log_2{128} = 7$