Additional steps needed to this formula to calculate multiple if scenarios...

Earlier I posted the following problem for a solution. I received an answer which is below and worked fine. However I need to add a few extra steps to this already given formula. I outlined what’s needed below the bold answer to the original problem.

A1 = an amount EXP: 350,000
B1 = % #1 EXP: 3.00%
C1 = % #2 EXP: 2.00% (sometimes this cell will not have a % entered)
D1 = Formula

I need 2 different scenarios considered.

1st: If only B1 has a % I would like D1 to simply calculate 3.00% * 350,000 =10,500

2nd: If both B1 and C1 have % entered, I would like B1 to only multiply the value in A1 up to 100,000. Then have C11multiply by the remaining value for a final answer in D1.

EXAMPLE: B1 would have calculated 3,000 (3.00% * 100,000) and C1 would have calculated the remaining amount of 5,000 (2.00% * 250,000) for a total of 8,000 in D1

ANSWER
=IF(C1="",A1*B1,(MIN(A1,100000)*B1)+(MAX(0,A1-100000)*C1))

I need to add a few steps to this answer from earlier.

It works great however now in addition to the formula, I need to multiply the answer from your formula against 3 different % valued cells depending on the text selected in a 4th cell. The 3 % cells sit on another worksheet.

In my original final example, D1 = 8,000.

D1 = 8000
K1 = a letter EXP: "F"
Worksheet!E1 = a % EXP: 25% and represents the letter "R" if imputed into K1
Worksheet!F1 = a % EXP: 50% no letter representation for this one-just standard calculation
Worksheet!G1 = a % EXP: 75% and represents the letter "F" if imputed into K1

So if I entered nothing into K1 the answer in D1 should be 4000 (8000*the percentage amount displayed in Worksheet!F1)
If I enter "R" into K1 the answer in D1 should be 2000 (8000*the percentage amount displayed in WorksheetE1)
If I enter "F" into K1 the answer in D1 should be 6000 (8000*the percentage amount displayed in WorksheetG1)