A woman wants to go from her house to a cabin as quickly as

A woman wants to go from her house to a cabin as quickly as possible. The cabin is situated 4 km down from the house on the opposite side of a lake with straight shorelines. The lake is 2km wide. She is planning first to run along the shore the distance of d km and then swim straight to the cabin. If she can run at 12km/h and swim at 4km/h, the distance d that minimizes travel time is?