Jon is given some money by his mother to pick up some milk at a local store. He walks slowly to the store at a rate of 3 km/h for 15 minutes, takes 5 minutes to buy the milk, and then runs home at a rate of 5 km/h. Create a graph to present this information and use the graph to determine how long the whole trip took.
I just need help solving the bolded part. What formula am I supposed to use to figure how long he made it back home at 5 km/h?