Answer:
24 minutes
Explanation:
we have information:
minutes of TV minutes of commercials
30 ⇒ 8
and we want know how many minutes of commercials there are in 90 minutes of TV:
minutes of TV minutes of comercials
30 ⇒ 8
90 ⇒ x
where x is the number of minutes of commercials, we solve this by the rule of three: multiply the cross quantities (90 by 8) and then divide by the amount we haven't used (30), like this

the answer is: 24 minutes