How Do I repeat a calculation until I cross a threshold in Google Sheets

Question

I have a Google Sheet I'm using to evaluate financial goals. In this sheet, I have 8 cells. The first two cells are used to enter parameters that are used by the formulas in the other cells.

The first cell is a parameter that generates the result in cell 7. The second cell is a threshold I want to reach. Basically, I want to take the value in cell 1 and increase it by 1 until the result seen in cell 7 crosses the value in cell 2. An example looks like this:

  A                        B
1 Current Total            $10000
2 Target Amount            $1000
3 Current Amount           =DIVIDE(B1, 100)
4 Result A                 =PRODUCT(B3, 0.35)
5 Result B                 =PRODUCT(B3, 0.50)
6 Result C                 =PRODUCT(B3, 0.15)
7 TOTAL                    =SUM(B4:B6)
8 Total Needed             ?

Using the example above, I want to create a formula that increases the value B1 by 1 until the value in B7 crosses the value in B2. I want to put the amount used to cross the threshold in cell B8.

I would prefer to do this repeat operation "behind the scenes" so only the result appears in cell B8. I don't want to show all of the "work". Is there a way to do this in a Google Sheet? If so, how?