-72*(1/4-5/9+7/12)/(-2)

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-72*(1/4-5/9+7/12)/(-2)
-72*(1/4-5/9+7/12)/(-2)

-72*(1/4-5/9+7/12)/(-2)
=-72X（9/36-20/36+21/36）/(-2)
=-72X（-11/36+21/36）/(-2)
=-72X(10/36)/(-2)
=-72X(-5/9)
=40