The answer is 3. What you are looking for is not a math, but a logic observation. Take a look are circles (empty spaces) in numbers. For example, 8809 has 6 circles: two in 8 + two in the second 8 + one in 0 + one in 9. That's why 8809 = 6. Similarly, 3590 has 2 circles: one in 9 + one in 0. Thus, 3590 = 2. You can check all examples if you want. Therefore, 9183 = 3 because 9183 has 3 circles: one in 9 + two in 8.