Isolated and Accumulated in report

Hi Experts,

Could you please anyone help me to solve this :

I want to display 6 months rolling for cost in report

Layout should be like this :

cal/month cost(Isolated) Cost(Accumulated)

M1 M1 M1

M2 M2 M1+M2

M3 M3 M1M2M3

Points will be assigned for correct answers

Regards