To calculate the instantaneous rate of change in Excel, you can use the slope function. Here are the steps:

1. First, create a third column next to your data (x) and (y) and label it "dy/dx" or whatever you prefer.
2. In the first cell of the "dy/dx" column, enter the formula "=SLOPE(B2:B3,A2:A3)".
3. Copy the formula down to the rest of the cells in the "dy/dx" column.
4. The formula will calculate the slope of the line between the current point and the previous point, giving you the instantaneous rate of change at that point.
5. The first cell in the "dy/dx" column will be blank since there is no previous point to calculate the slope from.
6. You can format the "dy/dx" column as a number with the desired number of decimal places to make it easier to read.

That's it! You now have the instantaneous rate of change for each value in (y) with respect to (x).