Answer
$c = 40$ m
Work Step by Step
RECALL:
In a right triangle,
$\sin{A} = \dfrac{\text{length of opposite side}}{\text{length of hypotenuse}}
\\\cos{A} = \dfrac{\text{length of adjacent side}}{\text{length of hypotenuse}}
\\\tan{A} = \dfrac{\text{length of opposite side}}{\text{length of adjacent side}}$
Use the sine formula to obtain:
$\sin{A} = \dfrac{\text{length of opposite side}}{\text{length of hypotenuse}}
\\\sin{30^o}=\dfrac{20}{c}$
Multiply $c$ to both sides of the equation to obtain:
$c \cdot \sin{30^o} = 20$
Divide $\sin{30^o}$ on both sides of the equation to obtain:
$c = \dfrac{20}{\sin{30^o}}
\\c = \dfrac{20}{0.5}
\\c = 40 \text{ m}$