Chapter 1 - Functions - 1.3 Inverse, Exponential, and Logarithmic Functions - 1.3 Exercises - Page 37: 61

$\log_{4}40=\dfrac{\ln40}{\ln4}\approx2.660964$

$\log_{4}40$ Apply the change of base formula, which is $\log_{b}x=\dfrac{\log_{a}x}{\log_{a}b}$, to express the given $\log$ in terms of the natural logarithm: $\log_{4}40=\dfrac{\ln40}{\ln4}$ Evaluate using a calculator: $\dfrac{\ln40}{\ln4}\approx2.660964$