Answer: sin (A) = 4 / 5
Procedure step-by-step:
1) The ratio sine is defined as opposite-leg / hypotenuse
2) From the figure, the opposite-leg to angle A is BC and it measures 28
3) From the figure, the hypotenuse is AB and its measure is 35.
4) Therefore sin(A) = 28 / 35.
5) Simplify dividing numerator and denominator by 7: 28 / 35 = 4 / 5