Question

Cindy has 42 meters of fencing. She plans to fence in a rectangular dog run that is 6 meters wide. How long can the run be made?

Answer 1

the Answer is 12

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Answer 2

So all sides together are 42 meters.
Two of the sides are 6 meters.
So 42-(2*6) = 30 is left for the other two sides, that's 15 meters per side.