Question 1131513
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Due south and due west are paths that are perpendicular to each other, so a triangle showing the planes' paths and the distance between the planes is a right angle.<br>
Observe that the two speeds are 420 = 140*3 mph and 560 = 140*4 mph.  So the right triangle is a scale model of the 3-4-5 right triangle; the distance between the planes is increasing at a rate of 140*5 = 700 mph.<br>
The number of hours required for the distance between the planes to be 3150 miles is<br>
{{{3150/700 = 4.5}}}<br>
ANSWER: It will take 4.5 hours for the distance between the planes to be 3150 miles.