If the 8-digit number is 789x531y is divisible by 72, then the value of (5x — 3y) is:

As per the given question,

789x531y is divisible by 72

The given number will be divisible by 72, if it is individually divisible by 8 and 9.

Divisibility by 8-Any number is divisible by 8if the last three digit of that number is divisible by 8.

last 3 digit is 31y, it will be divisible by 8 if  y=2

Divisibility by 9-Any number is always divisible by 9 if the sum of the digit of any number is evenly divisible by 9.

Hence, the required number $$= 7+8+9+x+5+3+1+y=33+x+y$$

Now, y=2

the required number $$=33+x+2=35+x$$

if x=1, then it will be divisible.

Hence the value of $$5x-3y=5\times 1-3\times 2=5-6 =-1$$