R is a vector orientated programming language. Thus, as far your your dataframes would be named sheet1, sheet2, ... with columms a, b, c, ...

equivalent

sheet0$a= sheet1$a

equivalent

sheet0$d= sheet1$b + sheet1$c

equivalent

sheet0$g= sheet1$f * sheet1$d

However, you are not restricted to stupidly reference data excel like in A, B, C columns any more. In R you can give each data column by an intuitive name and reference the data by it. E.g. sheet0$sales for the whole column and sheet0$sales[1] for the first cell of the column.