Answer
$a\approx13.6$ m
$b\approx14.7$ m
Work Step by Step
$\sin43^{\circ}=\frac{a}{20}$
$a=20\times\sin43^{\circ}$
$a\approx13.6$
Using Pythagorean Theorem to find $b$.
$b=\sqrt {20^{2}-a^{2}}$
$b\approx\sqrt{20^{2}-13.6^{2}}$
$b\approx14.7$