Total values in one column to equal value in another column.

[john3sixteen]

I hope that I can accurately describe what I'd like to do. I would be interested in any option (using just formulas in excel or using a macro). I want to pull the value in Column D into column C until the sum reaches the number in column C corresponding to the next blank cell in Column B. Then the process would restart for the next number in column C corresponding to the next blank cell in Column B. In my example, column C would have 2100 in the first row, 6300 in the second row, and 600 in the third row (of the 700 in column D), & either a blank or 0 in the next row to equal the 9000 in column C, next to the blank cell in column B. Then it would reset to do the same thing to equal the 20000 in column C, next to the blank cell in Column B. (putting 430, 5520, 7700, & 6350 of the 13150 in column C to total 20000) Then continue on down the sheet in this manner. Everything is a variable in this data set, and will change everytime, with the exception of the total to sum (using the values in Column D) will always be in Column C, next to the blank cell in Column B. Any help would be greatly appreciated.

Column B	Column C	Column D
100		2100
200		6300
300		700
400		11200
	9000	20300
1001		430
1050		5520
1221		7700
1365		13150
2088		1000
	20000	27800

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