To find the breadth of a river, an observer stands at a point B on one bank and notes a point A directly across on the opposite bank.

He then measures a distance BC of 36m in AB produced, and next walks a distance CD of 120m at right angles to AC.

He then finds that AC subtends an angle of 56 degrees 20 minutes. at D. Find the breadth of the river, and the angle which AB subtends at D.

I am having trouble interpreting this question.