It must be 21.3 feet.
The sides of the triangle given to us are the side opposite the angle to the ground, 20, and the missing side is the hypotenuse.
opposite/hypotenuse is the ratio for sine:
sin 70 = 20/x
Multiply by x:
x sin 70 = 20
Divide both sides by sin 70:
(x sin 70)/(sin 70) = 20/(sin 70)
x = 21.283 ≈ 21.3
