The answer is the difference between the largest and smallest number in each digits.

6 4 2 5 9

4 9 8 5 7 (-)

- -

2 5 6 0 2 ( Subtract Big - small number in each unit's , ten's , 100's place etc.)

- -

Similarly, on the given prb,

9 8 6 5 4

2 4 3 1 8 (-)

7 4 3 4 4

Answer is **74344**