Hello De'mareyia,
Let's call x the number of shirts Nate ordered.
He paid $7.90 per shirt so the money spent on shirts is 7.90 times x ---> 7.90x
He also paid $2 for shipping.
You're told Nate spent a total of $160 so the money spent on shirt PLUS the money spent on shipping equals $160: 7.90x + 2 = 160
To solve this equation, first subtract 2 on both sides: 7.90x = 158
Divide both sides by 7.90 ---> x = 158/7.90
Do that operation in your calculator and you will get 158/7.90 = 20
Nate ordered 20 shirts.
Cheers.