Norwood middle school spends $17 on each workbook in addition to a one-time shipping cost of $21. if the school recently spent $157 on a shipment of workbooks, how many workbooks did it buy?

You would make it into an equation then solve it after creating that equation. When you hear the word "each" that should give you a clue or a sense that should be a variable. So in this case it would be:
17x+21=157
Then you would solve it from there. Once you find x you'll know how many workbooks Norwood Middle School purchased.

Here is my answer, i'm sorry if you didn't understand my explanation