First of all you have two of them. Convert all inches to feet.
1 foot = 12 inches
2 feet = 24 inches.
30 inches is a little harder
30/12 = 2.5 feet. Now you are ready to figure the problem
Top A
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Area = L * w
L = 6 feet
w = 2 feet
A = 2 * 6 = 12 Square feet
Top B
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Area = 2.5 * 4
Area = 10 square Feet
Total Area = 10 + 12= 22 square feet
Cost
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Square feet * 42
Cost = 22 * 42
Cost = $924
