The ratio would be 3:1
( the 6 triangles are blue, which I’m pretty sure they are.)
Since there are 18 yellows and 6 blues, and the question calls for the ratio of the yellows to the blues, the ratio is 18:6. But you always have to simplify. The GCF is 6, so you would divide both of them by 6. The ratio is then 3:1.