Copy value

[gary]

If B4 = B3 and A3 contains a value, how can I copy the value in A3
down to A4?

Here is my spreadsheet:

A B
1 0082766
2 0082767
3 0082768 0082768
4 0082768
5 0082768
6 0082768
7 0082768
8 0104361
9 0104365
10 0104367
11 0104368
12 0104370
13 0104409 0104409
14 0104409

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This is the result I'm looking for:

A B
1 0082766
2 0082767
3 0082768 0082768
4 0082768 0082768
5 0082768 0082768
6 0082768 0082768
7 0082768 0082768
8 0104361
9 0104365
10 0104367
11 0104368
12 0104370
13 0104409 0104409
14 0104409 0104409