We could plug in the answer choices, which represent the distance between Car A and Car B.
In 2 hours, B travels r*t = 30*2 = 60 miles. In .4 hours, B travels r*t = 30*.4 = 12 miles. When we add these distances to the answer choices, the correct answer will show that if A doubles its rate, it will catch up to B in .4 hours.
Since one of the times given is .4 = 4/10, the correct answer likely will be divisible by 10. Let's skip over answer choice C and try B:
Answer choice B: distance between A and B = 20 miles.
In 2 hours, distance between A and B = 20+60 = 80 miles.
Thus, rate for A to catch up = d/t = 80/2 = 40 miles per hour.
A's rate doubled = 2*40 = 80 miles per hour.
In .4 hours, distance for A = r*t = 80*.4 = 32.
In .4 hours, distance for B = 20+12 = 32. Success!
The correct answer is B.
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