Question 1118717
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The lengths of the shortest and longest sides are given in terms of the length of the middle side; so logically we should use our variable x as the length of the middle side.<br>
x = length of middle side
x-71 = length of shortest side
x+379 = length of longest side<br>
To find x, the length of the middle side, write and solve the simple equation that says the perimeter (sum of the lengths of the three sides) is 3086.  Then use that value and the definitions above to find the lengths of the other sides.