Using Excel and need a little help with a simple formula.

I know conditional formatting should do the trick here, however, I need help creating the exact formula for my need.

In column A I write the expenses, i.e. 750, 260 etc. In column B I note which currency it is, i.e. EUR, GBP or USD.

What I need is for Excel to automatically format the numbers in column A as their respective currencies based on what I put in column B.

For example, if I enter "700" in column A, and then in the adjacent cell in column B I enter "USD", then the number "700" in column A should automatically be formatted as USD currency. If I put in GBP it should be formatted as GBP currency and so on.

Any help would be appreciated, thanks.