Question 82372
Since everything is is minutes, we'll first find the answer in minutes and then convert it to hours

In 1min Beavis and Butthead would have covered 15/60 miles = 1/4miles
In 5mins Beavis and Butthead would have covered 15/60 miles =5x( 1/4miles) = 5/4 = 1.25miles

Now the neighbour starts chasing them at 20miles per hour
Effective speed = 20-15 = 5miles per hour = 5/60 = 1/12mile per minute

Time taken to cover 5/4 miles = (5/4) / (1/12) = 15mins

Time taken in hours = 15/60 = 1/4 = .25hours