Question

if 9999=4, 8888=8 ,1816=6,1212=0, then 1919?

Answer 1

It means that 9999 has 4 circles so that (1 circle in each 9)

same in 2nd case that 8 circles in 8888 so that,  two circles in each 8.

1816 has 3 circles so that 2 circles in 8 and one circle in 6.

Zero circles in 1212.

and 1919 has 2 circles and it means that (One circle in each 9).

So that  1919 = 2