3. Use the digits 1 to 9 to form three three-digit numbers $\mathbf{a}, \mathbf{b}, \mathbf{c}$ (each digit can only be used once), then the maximum value of $a+b-c$ is ( ).


【Analysis】 $(a+b)$ is maximum, $\mathrm{c}$ is minimum, 9 and 8 are both in the hundreds place, similarly 7 and 6 are both in the tens place, 4 and 5 are both in the units place, $\mathrm{c}$ is then $123,975+864-123=1716$.