If 9999=4 8888=8 1999=3 2222=0 Then 1616=?

4 o=9999=4 8o=8888=8 3o=1999=3 2o=1616=2 ans is 2

HINT:you don't have to be a mathematical genius to solve just observe.............

if 3+4=21 , 5+6=55 , 2+7=18 then how much is 6+8=?