From the top of a cliff 30 m high, the angle of depression of a boat on the sea is 30°…

Step 1. The angle in the triangle. The angle at the boat is $30°$, equal to the angle of depression.

Step 2. (a) $\tan 30° = \dfrac{30}{d}$, so $d = \dfrac{30}{\tan 30°} = 30\sqrt{3} \approx 51.96\ \text{m}$.

Step 3. (b) $\sin 30° = \dfrac{30}{\text{line}}$, so the line of sight is $\dfrac{30}{1/2} = 60\ \text{m}$.