Three numbers a, b, and c are in between 2 and 18 such that 2a, b are in arithmetic progression, and b, c, 18 are in geometric progression.

a) a = 4, b = 6, c = 9
b) a = 5, b = 8, c = 12
c) a = 6, b = 10, c = 15
d) a = 7, b = 12, c = 18