The ratio 21:14 when divided by 7 on each side, is the smallest ratio that has the same value as 21:14. this becomes 3:2
then multiply both sides by a few different numbers on both sides each ,
for example, 3:2 is the same as 6:4 (3:2 times 2) 9:6 (3:2 times 3) 12:8 (3:2 times 4) 15:10 (3:2 times 5) and so on the ratio of the right number I divided by the left on all of them is 1.5