When mario has to leave the house for a while, he tethers his mischievous puppy to the corner of a 12 ft-by-8 ft shed in the middle of his large backyard. the tether is 18 feet long. which description fits the boundary of the locus of points in the yard that the puppy can reach?

a. semicircles of radii 18 ft, 10 ft, and 6 ft
b. a three-quarter circle of radius 18 ft, quarter circles of radii 12 ft and 8 ft
c. a three-quarter circle of radius 18 ft, quarter circles of radii 10 ft and 6 ft
d. semicircles of radii 18 ft, 12 ft, and 8 ft