Answer: 16 feet
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Step-by-step explanation:
The perimeter is the amount of fencing needed to enclose this trapezoid.
The known sides of the figure add to 11+6+11 = 17+11 = 28 feet
The entire peimeter is 44 feet, which means 44-28 = 16 feet are needed along the bottom side.
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If you want to involve algebra, then let x be the missing side
side1+side2+side3+side4 = perimeter
x+11+6+11 = 44
x+28 = 44
x = 44-28
x = 16