Chapter 1 - Foundations for Algebra - 1-9 Patterns, Equations, and Graphs - Practice and Problem-Solving Exercises - Page 64: 17

This is the relationship of Ty and Bea modelled as a a table, equation and a graph.

The table is simply increasing by 1 each with the initial difference between Ty and Bea being 3. This results in the equation $y=x-3$. The graph shows a visual depiction of how the relationship between the ages of Ty and Bea would look.