Answer
$a) \approx 11.77$
$b) \approx 9 . 55 \ in.$
Work Step by Step
a) We have the formula:
$L=9+5.1 \log (d)$
Plug in $d=3.5$ to obtain:
$L=9+5.1 \log (3.5) \approx 11.77$
b) We have the formula:
$L=9+5.1 \log (d)$
Plug in $L=14$ to obtain:
$14=9+5.1\log d \\ 5=5.1 \log(d) \\ \dfrac{5}{5.1}=\log(d) \\ d=10^{0.98} \approx 9 . 55 \ in.$
