How would we find out in real life how much each shirt cost? We'd subtract 7.99 from 71.83 and divide the difference by 3, right??
Let's work that backward. Let's say a shirt cost $6. Three would cost $3(6), or $18. Since each shirt costs $s, our price for 3 shirts is $3s. We have to add shipping to get a total, which we are given. When writing an equation, we leave out labels like $ or meters or books or whatever.
