How to fix formula

Hi everybody,

I am working SAP Project, I Have a small issue regarding one test i.e. Sulphated ash

Which Is having Consecutive weights

For example : 1 st MIC is weight of the crucible(W1) which is having sampling procedure 1

                       2 nd MIC is Weight of Crucible+Sample(W2) which is Sampling procedure 1

                       3 rd MIC is  weight of sample after 600 degree heat (W3) which is sampling procedure 1

                       4 th MIC is Final weight (WF)     which is Sampling procedure 5

                       5 th MIC is result          which is having sampling procedure 1 & Formula 

Here i want how to fix formula.