2/3s + 5/6s =21 solve for s as a whole number or simplest fraction !

Multiply every by 6
4s+5s=21
9s=21
S=21/9
Which reduces to
7/3

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.