```py
sheet = {"A": {}}
sheet["A"][1] = "monthly salary"
sheet["A"][2] = 3000
sheet["A"][3] = "yearly salary"
sheet["A"][4] = sheet["A"][2] * 12
```
```py
sheet = {"A": {}}
sheet["A"][1] = "monthly salary"
sheet["A"][2] = 3000
sheet["A"][3] = "yearly salary"
sheet["A"][4] = sheet["A"][2] * 12