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Explanation:
The units for each are in feet.
The formula tying together all three variables is
P = 2(L+W)
which is the same as saying
P = 2L+2W
We can think of it having two copies of L and two copies of W, four sides total, added together to get the full perimeter.
I'll go with the first version. Plug in the given values and solve for L
P = 2(L+W)
2(L+W) = P
2(L+144) = 580
L+144 = 580/2
L+144 = 290
L = 290-144
L = 146 feet is the length
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We can confirm this by saying
P = 2(L+W) = 2(146+144) = 2*290 = 580
Or we could say
P = 2L+2W = 2*146+2*144 = 292+288 = 580
or,
P = L+W+L+W = 146+144+146+144 = 580
