Enter Formulas Only On Subtotal Rows

a huge spreadsheet that is taking up way too much time. It starts out with 6,000-7,000 rows, but then, she does Subtotals & it grows to nearly 10,000 rows! Then she has to deal with each & every one of the Subtotal rows, by hand. Here is a small sample of the spreadsheet, after the Subtotals have been applied:

Manifest Dttm
Manifest No
Carrier Scac

[Code].....

This sheet has columns A-Q. The key columns for our purposes are K (Weight In Lbs), L (Pickup Charge) and M (Consolidation Charge). We need to add information to column R on each SUBTOTAL row only! On each row there will be an amount in EITHER column L or column M, but not both.

1) If the amount is in L and K is LESS than 488 then R needs to show 44.39.
2) If the amount is in M and K is LESS than 124 then R needs to show 3.82.
3) If either
a. The amount is in L and K is 488 or HIGHER or -
b. The amount is in M and K is 124 or HIGHER
THEN R needs to show a formula to do this: (L+M)/(K/100)

Is there a way to either put a formula in just the Subtotal rows to accomplish this or (preferably) have a macro enter either the 44.39, 3.82 or the formula? I was able to come up with a formula that gets the correct amount in col R. Here's my formula:

Code:
=IF(AND(M3=0,K3123))),SUM(L3:M3)/(K3/100))))))