`A = 1/3 - 3/4 - (-3/5) + 1/72 - 2/9 - 1/36 + 1/15`
` = 1/3 - 3/4 + 3/5 + 1/72 - 2/9 - 1/36 + 1/15`
` = (1/3 + 3/5 + 1/15) - (3/4 + 2/9 + 1/36) + 1/72`
` = (5/15 + 9/15 + 1/15) - (27/36 + 8/36 + 1/36) + 1/72`
` = 1 - 1 + 1/72`
` = 0 + 1/72`
` = 1/72`