$10 \times 9 + 6 \times 3 = 108$  $9 + 3 = 12$ 
In a magic land, a monkey wants to climb a tree of $180$ m. The monkey can make one of the two kinds of climb each day: $6$ m up or $10$ m up. Beginning at the ground , at least how many days will the monkey need in order to rest on the branch of $108$ m high? 

a. $$9$$ 
b. $$10$$ 
c. $$11$$ 
d. $$12$$ 
e. $$14$$ 