If Speed = dist/time, then;
dist = speed * time
We also know that both of them travel the same distance, so we equate the distance travelled to each other
36 * x+45 = 72 * x
36x + 1620 = 72x
72x - 36x = 1620
36x = 1620
x = 1620/36
x = 45 miles
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