Solve the Equation: Finding the Missing Number in 15 - □ = 9

To solve the problem $15 - \Box = 9$ using two jumps on a number line, we need to break down this subtraction into simpler parts.

If we think of the subtraction using two jumps, one effective strategy is:

• First, subtract 5 from 15 to reach the intermediate round number, 10: $15 - 5 = 10$.
• Second, subtract from the intermediate number, 10, to reach the target, 9: $10 - 1 = 9$.

Adding both jumps together, $5 + 1 = 6$. Thus, the missing number in the original expression is $6$.

The final solution to the problem is $\Box = 6$.