If an eleven-digit number 5y5888406x6 is divisible by 72, then whatis the value of (9x — 2y), for the least value of x?

First step take the easiest factor of 72

It's 12*6

Make your factor as smallest as that 

Again factorise it.. You will get only 2 and 3 

We all know the Divisibility rule of 2 and 3

For checking Divisibility of 2 we just need to check the unit number if it is even then that number will be divisible by 2

For checking Divisibility of 3 we just need to add all the numbers if the total is divisible by 3 then the whole digit will be divisible by 3.

So, 5y5888406x6 is our digit see the unit digit is even so it is divisible by 2.

5+y+5+8+8+8+4+0+6+x+6 =50

For making it divisible by 3 you should have to assume the number. If you select x as 1 and y as 3 then it will be 54 and divisible by 3.

Why we take x as 1 because our question says you have to take x as least number. 

So ans is 3