Chapter 7 - Exponential and Logarithmic Functions - 7-4 Properties of Logarithms - Practice and Problem-Solving Exercises - Page 467: 72

$\dfrac{\log_{10}{3x}}{\log_{10}{4}}$ or $\dfrac{\log{3x}}{\log4}$

Recall the change of base formula (pg. 464): $\log_{b}{m}=\frac{\log_{c}{m}}{\log_{c}{b}}$ Applying this formula to our equation ($b=4,m=3x,c=10$), we get: $\log_{4}{3x}=\dfrac{\log_{10}{3x}}{\log_{10}{4}}$