Question 519495
The planes are approaching each other at a combined 620 mph.  
When the converge, they will have traveled the 1860 miles.
To cover 1860 at 620 mph will take 3 hr.
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Check this answer to be sure they cover the 1860 miles.
220 mph * 3 hr = 660 miles
400 mph * 3 hr = 1200 miles
660 + 1200 = 1860 miles
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Done.