Pythagorean Theorm

You are at your grandma's house for the weekend but you've decided you're ready to go home. Your mom says that before you hop on your bike to come home, you must tell her exactly how many miles is the shortest distance from Grandma's before you can leave.  She tells you that your street and Grandma's street meet to form an L at your school.  Grandma's house is three miles east of the your school and your house is four miles north of your school.  She also tells you the shortest distance home does not involve passing your school again.  How can you do this? Why not let Pythagoras help you home?