A woman on an island wishes to reach point R on a straight shore on the mainland from a point P on the island. The point P is 9km from the shore and 15km from the point R. If the woman rows a boat at a rate of 3 km/h to a point Q on land, then walks the rest of the way at a rate of 5km/h, express the total time it takes the woman to reach point R as a function of the indicated angle