Since there are 60 minutes in an hour, to find out how many minutes are in 4 hours we have to multiply 4*60. 4*60=240, therefore there are 240 minutes in 4 hours.
This makes our ratio 240 minutes:30 minutes. To simplify this ratio into simplest terms, we have to find the GCF, or greatest common factor of 240 and 30 minutes. Because 240 is divisible by 30 and 30 is divisible by 30 as well, 30 is the GCF of 240 and 30. This means we should divide both parts of the ratio by 30.
240/30 : 30/30
When simplified, you get 8:1, which is your final answer.
Hope this helps!