It asks to "Find the unit price in dollars per padlock"
The phrasing "dollars per padlock" is the same as "dollars per 1 padlock"
In other words, the teacher wants to know how much 1 padlock costs.
7 padlocks : $23.80
7/7 padlocks : $23.80/7 .... divide both parts by 7
1 padlock : $3.40
We see that 1 padlock costs $3.40, so the unit cost is $3.40 per padlock
