I want to put in Column M the result of the number in Column L - that in
Column J - that in Column K.

If I was doing this in a worksheet, and using row 9 as an example, I would
type in M9 the formula =L9-J9-K9

For the life of me I cannot get this to work in VBA. I have tried various
variations of the following, none works.

Cells(i, "M") = Cells(i, "L") - Cells(i, "J") - Cells(i, "K")

I get "Type mismatch" error.

All I want to do is a simple subtraction!