According to the question, A number is divisible by 3 if the sum of the digit of that number is divisible by 3 . 672xy⇒6+7+2+&x+y =15+x+y Now, the possible values of x and y are x=1,y=2 and x=2,y=1 A number is divisible by 7 if the difference between twice the digit at ones place and the number formed by other digits is either zero or a multiple of 7 . Now, last two digit =xy=21×2=42 Now, difference =672−42=630, Which is divisible by 7 . ∴x=2 and y=1 Now, 6x+5y=6×2+5×1 =12+5=17