Answer
The answer is below.
Work Step by Step
$(a)$
$v=7$ lies between $v=5$ and $v=15$
$5+2=7=\frac{2}{10}+5$
$W C I \approx 19+\left[\frac{2}{10}\right](13-19)=19-1.2=17.8^{\circ} \mathrm{F}$
(b) $T=28$ lies between $T=25$ and $T=30$
$28=25+\sqrt{\frac{3}{5}}(30-25),$ so
$W C I \approx \left[\frac{3}{5}\right](25-19)+19=3.6+19=22.6^{\circ} \mathrm{F}$