Explanation:

Correct option 4: 39

688xy is divisible by 3,7 and 11
Concept used:
Divisibility rule of 3 - If sum of all digit of number is divisible by 3 then whole number is divisible by 3.
Divisibility rule of 7 - To make a pair of 3 from unit digit than subtract left over pair,
The result is divisible by 7.
Divisibility rule of 11 - Sum of odd digit place - Sum of even digit place = 0 or multiple of 11.
Calculation:
688xy is divisible by 3,7 and 11
For divisibility rule of 3, (x + y) = 2, 5, 8, 11
For divisibility rule of 11, (6+8+ y) - 18+ x) = 0 or 11
(14+ y)-(8+x) = 0 or 11
We take the value of y = 8 or x = 3
⇒(14+8) - (83) = 0 or 11
⇒(22-11) = 11 [divisible by 11]
So, the value of x = 3 and y = 8
Now,
(5x +-3y)=(5x3 + 3 x 8)
⇒ (15+24)
⇒39
:. The required value is 39