Two towns, P and Q, are connected by a straight road, 20 miles long. Traveling from town P to town Q, the speed limit changes: the first 5 miles are 30 mph, the next 10 miles are 50 mph, and the last 5 miles are 40 mph. Two cars, one starting from town P and one from town Q, move toward each other at the same time. They adhere strictly to the speed limits in each section. How far from town P, in miles, will the two cars meet?