From his house, Gavin could drive due north to get to his parents' house or he could drive due east to get to his grandparents' house. It is 8 kilometers from Gavin's house to his parents' house and a straight-line distance of 10 kilometers from his parents' house to his grandparents' house.
How far is Gavin from his grandparents' house?
a. 4 km
b. 5 km
c. 6 km
d. 12 km