On a certain day John decided to go school using his newly purchased skates. So, he left his house and skated 15 km northwards, then turned left and skated 7 km, then he took another left turn and skated 15 km, and then finally turned right and skated 13 km. How far exactly is his school from his house?

A

20 km

B

6 km

C

2 km

D

28 km