Sam walked for 15 minutes before Al started running after him, then he walked for another 10 minutes while Al was trying to catch up to him. Therefore Sam walked a total of 25 minutes. We also know that he walked at a speed of 3.2mph. 25/60 hours * 3.2miles per hour = 5/12 hrs * 16/5 mph = 80 / 60 miles = 4/3 miles
I did the math in fractions instead of decimals because in this case, 4/3 is cleaner than 1.333333.....
Now lets look at what we know about Al. He ran for 10 minutes. We also know that he ran 4/3 miles since he caught up with Sam and that's how long Sam had walked. If we put this information into an equation we can solve for Al's speed: 10 minutes * x miles per hour = 4/3 miles 1/6 hr * x mph = 4/3 miles x = 24/3 mph x = 8 mph