Question 341397
A=2(bh+hl+lb) 
Evaluate b when A=11750sq mm; h=25mm and l=75mm 
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11750 = 2(b*25 + 25*75 + 75b)
5875 = 25b + 1875 + 75b = 100b + 1875
100b = 4000
b = 40 mm