15. Find the value of $\sin \theta$ if the terminal side of $\theta$ lies on the line $5 y-3 x=0$ and $\theta$ is in the first quadrant.
(a) $\frac{3}{\sqrt{34}}$
(b) $\frac{3}{4}$
(c) $\frac{3}{5}$
(d) $\frac{4}{\sqrt{34}}$
15. $\mathrm{A}$