Movie tickets at a local theater cost $6 for adults and $2 for children under twelve. if 175 tickets were sold, with cash receipts of $750, how many children's tickets were sold?

6x + 2y = $750

6(?) + 2(?) =
? + ? = 175

$6(100)= $600
$2(75)= $150
$600 + $150 = $750
100 + 75 = 175

100 adult tickets and 75 children’s tickets were sold.

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.