You are building a (rectangular) pool in your backyard. It measures 30m in the north-south direction and 25 meters east-west. (Some pool!) The bottom of the pool is a slanted plane so that it's 1m deep along the southern edge and 10m deep along the northern edge. (As I said, some pool!)
To build the pool you compute the angle of depression of a line from the southeast corner to the northeast corner. It is degrees,