Hi, Chong Siao Chuen
Thank you for using Microsoft products and posting them to the community.
You can create a secondary column:
In cell C2 (next to the first “Sales Amount”), enter =B2.
In cell C3, enter =C2+B3.
Drag this formula down next to the Sales Amount column to create a cumulative sum.
Determine the target date:
Once you have a cumulative sum, find the first cell in column C that has a value of 30,000 or more.
The corresponding date in column A is the date you are looking for.
I hope the above information can help you. Feel free to send a message if you need further help.
Best wishes
Aiden.C - MSFT |Microsoft Community Support Specialist