Two Search-And-Rescue Teams Leave Base Camp at the Same Time $6 \mathrm { hr }$

Two search-and-rescue teams leave base camp at the same time, looking for a lost child. The first team, on horseback, heads north at 4 mph, and the other team, on foot, heads south at 1.5 mph. How long will it take them to search a distance of 22 miles between them?

A) $6 \mathrm { hr }$
B) $3 \mathrm { hr }$
C) $4 \mathrm { hr }$
D) $5.5 \mathrm { hr }$
E) $4.5 \mathrm { hr }$