Question

If 21y5 is a multiple of 9

Answer 1

If 21y5 is the multiple of 9 then 2+1+y+5 is the multiple of 9 then 8+y is the multiple of 9 then
8+y= 9
y= 9-8
y= 1

Answer 2

21y5 is a multiple of 9 .
2+1+y+5=8+y should also be a multiple of 9
8+y=9or18or27 or 36 and so on
8+y =9 ; y= 1
Since y is a digit , so y is 1