larry starts at the bottom of a long staircase. he climbs exactly 2/3 of the stairs. then he goes back down exactly 1/2 of the way to the bottom. from that spot he climbs exactly 2/3 of the way to the top. finally from there he climbs 6 stairs to reach the top. how many stairs are in the staircase?

2 answers

18
9+10=21