Michael,
I can show you two ways to approach this problem.
Method 1:
You want to spread 25 item evenly over 7 days so divide 25 by 7 to see how many to asign to each day. $\frac{25}{7} = 3$ with a remainder so you can't quite assign 4 to each day. If you assign 4 to 6 of the days how many will you have for the seventh day?
Method 2:
Think of this as a number if items being evenly spread over 7 days and then on one of the days, 3 items are removed. The resulting number of items distributed on the 7 days is 25.
If $n$ is the number of items originall distributed to each of the 7 days then the process described above yields
\[7 n  3 = 25.\]
Solve for $n.$ When you have found $n$ make sure you check that it works.
Penny
