Chapter 4 - Exponential and Logarithmic Functions - Section 4.4 Logarithmic Functions - 4.4 Assess Your Understanding - Page 322: 101

$\dfrac{\ln{8}-5}{2}$

$\because e^y=x \text{ is equivalent to } y=\ln{x}$ $\therefore e^{2x+5} = 8 \text{ is equivalent to } 2x+5=\ln{8}$ Solve the equation above to obtain: \begin{align*} 2x+5&=\ln{8}\\\\ 2x&=\ln{8}-5\\\\ x&=\dfrac{\ln{8}-5}{2}\end{align*}