As per divisibility rule of 11,
$$9+7+8+7=3+x+y$$
or,$$31=3+x+y$$
or,$$x+y=28$$
but ,x and y are single digit number they can take a maximum value of 9 .
if both the digits are 9 then it can't be divisible.
So,either x or y is equal to 9 or 8.
So, the maximum value of x+y is 17.
D is correct choice.
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