Answer
$x = \frac{\log 23 - \log 4}{\log 2}$
$x \approx 2.52$
Work Step by Step
$20 = -3+4(2^{x})$
$20 + 3 = 4(2^{x})$
$23 = 4(2^{x})$
$\frac{23}{4} = 2^{x}$
$\log \frac{23}{4} = \log 2^{x}$
$\log \frac{23}{4} = x\log 2$
$x = \frac{\log \frac{23}{4}}{\log 2}$
$x = \frac{\log 23 - \log 4}{\log 2}$
$x \approx 2.52$