It takes 5 minutes for Frankie to get to school.
Solution:
Given that Time taken by traci to get to school = 12 minutes
Also given that It takes Antonio 3 more minutes to get to school than traci.
So time taken by Antonio to get to school = Time taken by traci to get to school + 3
=> Time taken by Antonio to get to school = 12 + 3 = 15 minutes.
Also given that trip to school is 3 times as long as Frankie.
Means Antonio takes 3 times more time that Frankie.
Let assume time taken by Frankie = "x" minutes
=> Time taken by Antonio = 3 times of time taken by Frankie =

But we have calculated earlier that time taken by Antonio = 15 minutes
=> 3x = 15 minutes
=>

Hence it takes 5 minutes for Frankie to get to school.