Number 888x53y4 is divisible by 72 we can write 72 as 8×9. Divisiblity of 8→ If last 3 digit is divisible by 8 then given number is also divisible by 8. ⇒
3y4
8
put y=8 (maximum) ⇒
384
8
⇒48 The value of y is 8 . Divisibility of 9⇒ If sum of digit is divisible by 9 so the number will be divisible by 9 . ⇒888x53y4 ⇒8+8+8+x+5+3+8+4 ⇒44+x⇒ If we put x=1 So, 45 will be divisible by 9. Put value of x=1 and y=8 in (7x+2y) ∴(7x+2y)=(7×1+2×8) =7+16=23