9514 1404 393
Answer:
 3.0
Explanation:
The angle, its opposite side, and the hypotenuse are given. Then the relevant trig relation is ...
 Sin = Opposite/Hypotenuse
 sin(21°) = x/8.3 . . . . . . . . . . . . . . . . . . use the given values
 x = 8.3·sin(21°) ≈ 8.3×0.3584 . . . . . . multiply by 8.3
 x ≈ 3.0