Calculating price increasings in Numbers

I have a finances spreadsheet for keeping track of home finances. I track electricity and gas costs, and want to know how to enter a % increase.

For example, I have £0.34 in cell A1as the current unit cost, which is formatted for sterling, and B2, for the cell that I physically type in the new unit cost amount.

The unit cost in A1 remains the same, but when I have inputted the new unit cost in B1, I want to C1 to show me the percentage increase as a %.

I can't seem to get the write formula in C1!

Any ideas?

Thanks.

Simon.