Sure, I can help you with that!

Here's the formula you can use to round the interest rate to the nearest eighth:

Assuming the original interest rate is in cell A1, this formula multiplies the interest rate by 8, rounds the result to the nearest whole number, and then divides the result by 8 to get the rounded interest rate to the nearest eighth.

To break it down further, the ROUND function takes two arguments: the first argument is the number you want to round, and the second argument is the number of decimal places to round to. In this case, we want to round to 0 decimal places, so we use 0 as the second argument.

Then, we divide the rounded result by 8 to get the interest rate to the nearest eighth.

1. For example, if the original interest rate is 6.89, the formula would calculate:
   
   Code:

   =ROUND(6.89*8,0)/8

   Code:

   =ROUND(55.12,0)/8

   Code:

   =55/8

   Code:

   =6.875

   So the rounded interest rate would be 6.875.
   
2. If the original interest rate is 6.91, the formula would calculate:
   
   Code:

   =ROUND(6.91*8,0)/8

   Code:

   =ROUND(55.28,0)/8

   Code:

   =55/8

   Code:

   =6.875

   In this case, the difference between 7.00-6.91 and 6.91-6.875 is the same, so the formula rounds to 6.875, which is the lower of the two options.

I hope that helps!