In the course of one five-month period, the water level of a lake went down 6 in., up 12 in., down 3 in., down another 16 in., and up 4 in. How much had the lake level changed at the end of the five months?
12 + 4 = 16 up
6 + 3 + 16 = 25 down
25 - 16 = ?