Question 1133365
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You have received two responses showing different ways to solve the problem algebraically; there are many others.<br>
But unless an algebraic solution is required, algebra is overkill for this problem; it is easily solved with logical reasoning and a bit of simple mental arithmetic.<br>
If the two cars are traveling for the same amount of time and the first car travels twice as fast as the second, then the first car travels twice as far as the second.<br>
If after 3 hours the 2 cars are 90 miles apart, that means the second car has gone 90 miles and the first car has gone 180 miles.  So the slow car is traveling at 90/3 = 30mph and the fast car is traveling at 180/3 = 60mph.