$\frac{391}{299}$=$\frac{391:23}{299:23}$=$\frac{17}{13}$
$\frac{615}{399}$=$\frac{615:3}{399:3}$=$\frac{205}{133}$
$\frac{456}{513}$=$\frac{456:57}{513:57}$=$\frac{8}{9}$
$\frac{759}{858}$=$\frac{759:33}{858:33}$=$\frac{23}{26}$
$\frac{31914}{42552}$=$\frac{31914:10638}{42552:10638}$=$\frac{3}{4}$