A-15 = B; a divided by 3 = B-6

A-15 = B; a divided by 3 = B-6

Substituting B = A-15 into a and dividing 3 = B-6, we get
Methyl division 3 = (A-15) - 6
A division 3 = A-21
Multiply both sides by three at the same time, and you get
A = 3a-63
Transfer, get
63 = 2A
So,
A = 31.5,
B = A-15 = 31.5-15 = 16.5
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