Answer
$3−\log_5{y}$
Work Step by Step
RECALL:
(1) $\log_b{\frac{M}{N}}=\log_b{M}-\log_b{N}$
(2) $\log_b{(b^x)}=x$
Use rule (1) above with $M=125$ and $N=y$ to obtain
$=\log_5{125}-\log_5{y}
\\=\log_5{(5^3)}-\log_5{y}$.
Simplify the first term by using rule (2) above to obtain
$=3−\log_5{y}$
