HELP. Trying to get a average spreadsheet for my darts team but only until they got 100

Morning,

I have been on this for sometime now, but I can't find out a way to do this.

I am in a darts team and we want to find our average for the darts thrown but only until they have 100 points left. But continue scoring for record how many darts are thrown to finish the game and the checkout score.

Example
A. B
1 Score Left 0.
2. 3 Darts 43
3. 6 Darts 100
4. 9 Darts. 40
5. 12 Darts. 33
6. 15 Darts. 43
7. 18 Darts. 72
8. 21 Darts. 60
9. 24 Darts. 78
10. 27 Darts. -
11. 30 Darts. 32


Cell B1 contains =($B$36)-(SUM(B2:B11)
B36 contains 501.

B1 continues to update itself as in fill in the cells below it with the score thrown counting down to 0 from 501.

I would like another cell to show the average score thrown for 3 darts until B1 goes less than 100. But to include the 3 darts thrown to put the score under the 100.

I know the average should be for the 24 darts thrown is 59. But for my life I can't work out how to only do the average until the score left goes below 100.

If anyone can help. This would be great.

Hi, thanks for your help nathansav.

I have worked out what i needed to do with your example.

I have attached the final product.

there are a few cells under the table with the font color as white. if you wanted to see the full thing.

kind regards