marlan is in the middle of a dense forest and needs to make it to the nearest town, which is 18 km north and 21 km east of his current position, as shown in the diagram below. he is travelling on his four wheeler, and can move at a speed of 6 km/h through the forest, and 36 km/h on the road. measured as a distance from town, at what point should he emerge from the forest and join the road in order to minimize his travel time?