Answer
$r(x)=9.4 $ $then$ $ x\approx3.537$
$r(x)=30 $ $then$ $ x\approx5.511$
Work Step by Step
Solving the equation $r(x)=y$, then we have:
$r(x) = y ⇔ 2\ln1.8 (1.8^{x})=y ⇔ \ln1.8(1.8^{x})=\frac{y}{2} ⇔ 1.8^{x}=\frac{y}{\ln(1.8)*2}$
$⇔e^{x\ln1.8}=\frac{y}{\ln(1.8)*2} ⇔ x\ln1.8=\ln(\frac{y}{\ln(1.8)*2})⇔$
$x=\ln(\frac{y}{\ln(1.8)*2}):\ln1.8$
For $y=9.4$ $then$ $x\approx3.537$ and for $y=30$ $then$ $x\approx5.511$
