Make double digits to single digit, like 16 in 1st row becomes 7.Arrange all numbers in single digit.
Now add each row. First 2 rows give same answer, so we expect last 2 rows to have same answer.
8+7+1=16
3+8+5=16
4+?+9=15(should be)
8+5+2=15.
So, ?=2