Answer
(a) $4$
(b) $5$
(c) $\frac{1}{16}$
Work Step by Step
(a) Use the formula $b^{log_by}=y$, we have $x=3^{log_34}=4$
(b) Use definition, $log_x(25)=2$ is equivalent to $x^2=25$, thus $x=5$ (discard negative answer).
(c) Use definition, $log_4(x)=-2$ is equivalent to $x=4^{-2}=\frac{1}{16}$
