"israel" wrote:
I have a value of (A) 642 and a value of (B) 385.20.
The difference is 256.80 what formula would I use
to find the percentage of value 256.80

If you want the percentage increase from 385.20 to 642, then:

=A1/B1 - 1

formatted as Percentage. You can also write =(A1-B1)/B1.

If you want the percentage decrease from 642 to 385.20, then:

=B1/A1 - 1

You can also write =(B1-A1)/A1.

If you want something else, it would help if you gave a numerical example as
you worked it out on paper; that is, "show your work".