1. **State the problem:** We need to find the sine of angle $B$ in a right triangle $BCD$ where $\angle C = 90^\circ$. 2. **Recall the sine definition:** In a right triangle, $\sin(\theta) = \frac{\text{opposite side}}{\text{hypotenuse}}$. 3. **Identify sides relative to $\angle B$:** - Opposite side to $\angle B$ is $CD = 70$. - Hypotenuse is the longest side $BD = 74$. 4. **Calculate $\sin(B)$:** $$\sin(B) = \frac{CD}{BD} = \frac{70}{74}$$ 5. **Simplify the fraction:** $$\sin(B) = \frac{\cancel{2} \times 35}{\cancel{2} \times 37} = \frac{35}{37}$$ 6. **Final answer:** $$\sin(B) = \frac{35}{37}$$