Two right circular cylinders have equal volume. The first cylinder has a radius of $6$ inches and a height of $12$ inches. What is the number of inches in the height of the second cylinder if its radius is $18$ inches? Express your answer as a mixed number.
volume of 1st = π(36)(12) = 432π
volume of 2nd = π(64)h
64π h = 432π
h = 432π/(64π)