Use a calculator to find sin 39°: d/30 = 0.6293... Multiply both sides by 30: d = 0.6293… x 30 d = 18.88 to 2 decimal places. The depth "d" is 18.88 m. Exercise. Try this paper-based exercise where you can calculate the sine function for all angles from 0° to 360°, and then graph the result. It will help you to understand these relatively ...