Need to formulate trigger once a certain value or milestone or threshold has been reached

Hello all,

I've stumbled upon a certain problem and have to solve it by using function/formulas. Any help would be greatly appreciated.

Let's assume, Jack and Mike have a joint account and they deposit their daily earnings everyday. Jack deposit his money ahead of Mike everyday.

'Who' earns 'What amount' at 'which' day is depicted in the attached spreadsheet.

Screenshot_2.jpg

The problem is:
1) Finding out who broke the 1000, 2000, 3000, 4000 and 5000 milestone/threshold first
2) Finding out in which days the thresholds have been broken

That's about it. Thanks a lot in advance!