Aptitude - Numbers - Discussion

I don't understand that equation. Please someone explain.

No. divisible by 9 is also divisible by 90,

Apply the divisibility rule of 9 and consider the simplest value of x and y which should be divided by 9.
eg. divisibility rule of 9 (x=2,y=2).
6+5+3+2+2 = 18
2+2 = 4 Ans.

653xy is divisible 90. It means 9*10 or 10*9.

Here we take 9*10. Therefore take x multiple as 9 and why multiple 10.
If the number is a multiple of 10 means the unit digit should be 0.
Therefore take y=0.

Now, x multiple is 9 then the sum of 653xy should be divisible by 3.
653xy= 6+5+3+x+y=14+x+0 (. Y=0).

Then 14+x then is take x=0 then x=14 not 3 divisible, x=1 then x=14+1==15 not 3 divisible,
Then x=14+2=16 not 3 divisible,
x=14+3=17 not 3 divisible, x=14+4=18 divisible of 3,
Therefore x=3.
The answer is x+y=3+0=3.