Triangles ABC and XYZ are similar, so the corresponding angle to A in XYZ triangle is angle X. We can actually find sin(X) very easily.
Because we know all sides and the right angle, we can use certain formula to find sin(X), like this:
sin(X) = opposite side / hypotenuse = 6/10 = 3/5
sin(X) = sin(A)
The correct answer is sin(A) = 3/5.