7. (10 Pts) A life guard is sitting at her station on the shore of a lake and a swimmer in the lake is in stress. The swimmer is 100 yards down the shore and 30 yards into the lake from there. The lifeguard can run about 3.5 yards/second and swim about 1.5 yards/second. How far along the shore should the lifeguard run to minimize the time it takes to get to the swimmer?