Answer
$\log _{4} 19 \approx2.124 $
Work Step by Step
Recall the change-of-base formula for logarithms:
$$\log _{b}{a}=\dfrac{\log _{m} a}{\log _{m} b}$$
Most scientific calculators only has natural logarithms and log base $10$.
Using the formula above and logarithm base $10$ gives
$$\log _{4}{19}=\dfrac{\log _{10} 19}{\log _{10} 4}$$
Using calculator yields
$$\log_4{19}\approx2.124 $$
