How to get the max Category name of a calculated field

[QS21]

Hi All,

I have the data as below, I have a calculated filed called Variance (formula given below). I need the category name that contributed to the downfall or improvement of total value compared to last month. Please help!

Month	Cat	Value
Jan	A	74
Jan	B	56
Dec	A	77
Dec	B	66
Variance	9%	Decreased from dec to jan
Contributed by B	15%
Variance formula	Sum(<dec value>-<jan value>)/<dec Value>