Answer
$\dfrac{\log_{10}{20}}{\log_{10}{12}}\approx 1.21$
Work Step by Step
Recall the change of base formula (pg. 464):
$\log_{b}{m}=\dfrac{\log_{c}{m}}{\log_{c}{b}}$
Since most calculators use base $10$ logarithms ($\log{x}=\log_{10}{x}$), we can evaluate the expression by rewriting it in base $10$ and using a calculator:
$\log_{12}{20}=\dfrac{\log_{10}{20}}{\log_{10}{12}}\approx 1.21$