What numbers replace A and B on the number line?

The arrow indicates that starting from A and adding 5 results in 4.

$$A + 5 = 4$$

To find A, subtract 5 from both sides:

$$A = 4 - 5$$ $$A = -1$$

The arrow indicates that starting from 4 and adding 8 results in B.

$$4 + 8 = B$$ $$B = 12$$

The numbers that replace A and B are:

• A = $\boxed{-1}$
• B = $\boxed{12}$