I have a data sheet that looks like this...

col a col b
abc 10
20
45
efg 5
18
10

I need it to look like this...
col a col b
abc 10
abc 20
abc 45
efg 5
efg 18
efg 10

since there is no consistency to the number of rows in col b with data, i
have to come up with a formula that is dynamic

The file has 20,000 rows so doing it manually is not the way to go.

Thanks