Calculating price range given the price and token amounts

[reuptaken]

Sorry for asking this basic question but I studied math last time 30 years ago, so I'm struggling.

My problem is:

I have a range (A0, B0) with some token amounts (x, y) and there's price ( P )

What I'd like to do is to move those token amounts to a different range (A1, B1), keeping the same token amounts and price.

A1 is a given value. How do I calculate B1?