Bart would like to visit Milhouse but they live on different sides of a 4km wide river so Bart must take a land taxi (that costs $5/km) for part of the trip and a water taxi that costs $15/km) for the remainder of the trip. Bart lives on the west side of the river at point B and Milhouse lives on the east side across from point A. Point A is 10km South of point B. What is the cheapest way for Bart to get to Milhouse?