From the way you worded the question I’m pretty sure you know how to do it, just like the wording and stuff is confusing.
So you need to figure out the youngest 25% of passengers. And then, you will figure out what the oldest age of that is.
So the issue you run into here is the whisker plot doesn’t actually tell us the ages of each specific passenger. So if you know that, you’ll be able to figure it out :)
If it doesn’t say, then let’s just put 60/4
(Because 75 is the oldest age and then you subtract 15 and %25 is 1/4 of 100) and then whatever number you get, you add back 15.
So 60/4 is 15. So then you add back 15 and that equals 30!
So if that’s all the info they’ve given you, then it will be 30. :)