The oldest date at which total customer's exposure becomes greater than 100

In simplified example, I have 3 clients with several loans each.
I have to add one more column which has to show the date at which customer's total loan exposure becomes greater than 100.
For example, exposure for customer A becomes greater than 100 on 5/1/2014, for customer B on 4/1/2014, for customer C on 10/01/2014.
Can you help me to set up formula in column D?

Problem1.xlsx

Thanks

1. Sort the table.
2. D2, copied down:

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3. E2, copied down:

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