Ans : 2

Solution 1:

Counter the number of circle in each digit and add them.

```
9999 = 4 (each 9 has 1 circle)
8888 = 8 (each 8 has 2 circles so 2 x 4 = 8)
1816 = 3 (8 has one circle and 6 has 1 so 2)
1212 = 0 (no circles in 1 & 2)
Hence,
1919 = 2 ( 2 circles of the number 9)
```

Solution 2:

```
9999 = 4 ... each 9 is equal to 1 so (1 + 1 + 1 + 1 = 4)
8888 = 8 ... each 8 is equal to 2 so (2 + 2 + 2 + 2 = 8)
1816 = 3 ? (what is the value of 1 and 6) ------------------------ equation (1)
1212 = 0 ... so the value of 1 and 2 is 0 ( 0 + 0 + 0 + 0 = 0)
put the value of 1 in equation 1
we'll get 6 = 1 i.e ( 0 + 2 + 0 + 6 = 3)
Hence,
1919 = (0 + 1 + 0 + 1 = 2) //by replacing the value of 1 and 9 with 0 and 1.
Ans is 2
```