Question 486214
robbers speed = 71 mph

police speed = 80 mph

catch up speed = 80-71 = 9 mph

12 minutes = 1/5 hour

in 1/5 hour the robbers travel 1/5 * 71 = 71/5 miles

..
time = (71/5 )/ 9
time = 71/5 * 1/9 
time = 71/45 
time = 1.578 hours