[16.5+7.2x55/7x(12.5/100-1/8)]/15/19
=[16.5+7.2x55/7x(0.12/100-0.125)]/15/19
=16.5÷15/19
=15x1.1÷15/19
=1.1x19
=1.1x20-1.1
=22-1.1
=20.9
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