How do I do this Optimization Problem?

A water line runs from east to west. A town wants to connect 2 new housing developments to the line by running lines from a single point P to the two developments. One development is 3 miles south of the existing line; the other development is 4 miles south of the existing line, and 7 miles east of the 1st development. Find the place on the existing line to make the connection to minimize the total length of the new lines.