Answer
$b = 15$
Work Step by Step
$A = \frac{1}{2} \times h \times ( b + B)$
$156 = (0.5) \times (12) \times (b + 11)$
$156 = 6(b+11)$
$156 = 6b + 66$
$90 = 6b$
$b = \frac{90}{6}$
$b = 15$
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