#### Answer

$\sin (B)=\frac{3}{5}$

#### Work Step by Step

The sine of an angle in a right triangle is the ratio of the opposite side to the adjacent side. The side opposite $B$ has a measure of $6$, and the hypotenuse has a measure of $10$. When we write these in a ratio, we get $\frac{6}{10}$, which simplifies to $\frac{3}{5}$.