Ratio of two quantities can be calculated only when they are of same units.
So, converting 3minutes54seconds into seconds, we get 3×60+54=234seconds
And, converting 2minutes6seconds into seconds, we get 2×60+6=126seconds
Ratio of given quantities =234:126
Simplifying it by dividing by 6, we get the ratio =39:21
Further simplifying it by dividing by 3, we get the ratio =13:7