Carry Data over

I need help in carrying data over.
if the total of a sum is 124 units, how do I get it to calculate the amount owed if every 25th units starts with a new price.
example is that the first 25 units cost 10. the second 25 units cost 12, the 3rd 25 units is 14 and so on.

i added an excel sheet that might explane more.

hope you can help.