specific addition

[studentofstone]

I need to set each cell in a column to sum two cells on its row. Such that each cell in column d is the sum of specific cells in its row.

  A   B    C    D
1  2    hi   3    a1+c1
2  3    go  4    a2+c2 
3  7    ha  9    a3+c3

it is a long list and I would like to not type make the equation for every cell.