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A pair of kids and a pair of adults decided to compete in a three-legged race. The kids got to start 21 meters ahead of the adults, since they had shorter legs. When they were told to start, the kids hobbled forward at a rate of 1 meter per second, and the adults hobbled after them at a rate of 4 meters per second. Soon they were side-by-side. How long did that take? How far did the adults go?

Setting up 2 equations:

$y=x+21$

$y=4x$

$4x=x+21$

$3x=21$

$x=7$

$y=28$

x=time and y=distance

The answer: it takes 7 seconds and the adults go 28 meters