Solutions by everydaycalculation.com
640 - 140 is 18.
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Related: 12/40-1/40 6/40-2/40 6/80-1/40 6/40-1/80 18/40-1/40 6/40-3/40 30/40-1/40 6/40-5/40 42/40-1/40 6/40-7/40
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