I am trying to set up a formula each time the data changes in column A
without having to do it manually.

The formula would be using two other columns of data for the rows involved
with the same company.

e.g.

   Column A                 Column Y

 2 Company ABC

 3 Company ABC

 4 Company ABC        =SUM(W2:W4)/SUM(R2:R4)

 5 Company def

 6 Company def

 7 Company def

 8 Company def        =SUM(W5:W8)/SUM(R5:R8)

 9 Company xyz

 10Company xyz        =SUM(W9:W10)/SUM(R9:R10)