If the drainage area is 1100 km 2 , estimate what fraction of the precipitation is lost via processes such as evapo- ration, deep groundwater infiltration, and consumptive use.

Hey there!

Remember that all of interior angles of a triangle add up to 180°. We can subtract our two angles from 180 to give us our third angle.

180-90-40=50

Therefore, ∠A=50°.

You can also check your answer using trigonometry. Using ratios you find that the side BC is about 19.04, and you find the arctangent of 19.04/16, which is about 49.998, which matches our angle.

I hope this helps!