One way to figure this out is to you can set up two equivalent fraction problems to figure out in both cases how many times the adult and twelve year old each blink in 60 minutes.
Adult blinks: [tex] \frac{450}{30} = \frac{?}{60} [/tex]
Child blinks: [tex] \frac{150}{15} = \frac{?}{60} [/tex]
In the "adult blinks" problem, you know that 30 is half of 60 - you can then multiply the numerator 450 x 2 to get 900 blinks per 60 min.
In the "child blinks" problem, 15 is one-quarter of 60, so you can multiply the numerator 150 x 4 to get 600 blinks per 60 min.
You can then just subtract the two new numerators, 900 - 600, to find that the adult blinks 300 more times than the 12-year-old in 60 minutes.
