How do you use an equation to model and solve a real-world problem?

Here's an example sally went to the store and got 13 apples when she got home her family ate 3 of the apples sally decides to go back to the store and get 5 more apples and when she returns home 3 more apples are gonna how many apples does sally have? the equation would be 13-3+5-3=12 so she has 12 apples and this represents the real world