How to find a target value from a list of calculated and ordered values

[gmatoka]

Please see attachment. I have a list of values, D2:02 that are calculated by adding a monthly contribution found in B2 to the previous month's balance.
Is there a formula/calculation that I can place in B4 that will return the first month that the goal can be obtained? For example, if the goal was $70,000,
then Jun-15 should be returned.

Thank you.