Answer
$\frac{1}{2}$
Work Step by Step
The power rule for logarithms says that $\log_b{M^p}=p\log_bM$ i.e. the logarithm of a number with an exponent is the exponent times the logarithm of the number.
Also $\log_a a^n=n$ if $a\ne1,a\gt0$.
Hence here: $\log_{16}{4}=\log_{16}{16^{\frac{1}{2}}}=\frac{1}{2}$
