The area A of a trapezoid is the height h times the average of the parallel bases a and b.
A = (1/2)(a + b)h
Solving for a,
2A = (a+b)h
2A/h = a+b
a = 2A/h - b
We have A=59.64, b=4, h=8.4
a = 2(59.64)/8.4 - 4
a = 10.2 yards
Answer: 10.2
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