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Explanation:
Recall that the opposite sides of any rectangle are the same length.
This means the top and bottom sides are the same length
top = bottom
2x+17 = 6x+9
2x-6x = 9-17
-4x = -8
x = -8/(-4)
x = 2
Then we can find each side:
We get the same length for top and bottom (21), which confirms the correct x value.
This is a 7 by 21 rectangle with area = length*width = 7*21 = 147 square units.