A car starts at {{s1.start}}. It moves by {{s1.change > 0 ? '+' : ''}}{{s1.change}}.
To add fractions, the pieces must be the same size.
Now that pieces are the same size, combine numerators.
A negative (red) and positive (blue) cancel out!
Solve the final equation using what you learned.
You've successfully added and subtracted rational numbers by finding common denominators and canceling zero pairs!