## Explanation

At the core, the OFFSET function delivers a range of 3 cells to SUM, which returns a summed result.

The arguments for OFFSET are provided as follows:

For **reference** we use the first cell in the data range, B5, entered as a mixed reference (column locked, row relative).

For **rows**, we use 0, since we don't need to change rows.

For **cols**, we use the expression:

```
(COLUMN()-COLUMN($O$5))*3
```

This part of the formula figures out how many columns from the starting reference to offset. In O5, the offset is zero, in P5, the offset is 3, and so on.

Finally, **height** is input as 1 and **width** is input as 3, since in this case we always want a 1 x 3 range of cells.

*Note: change 3 to the multiplier you need, shown as "n" in the generic form of the formula above.*