Jeff writes comic strips for a local newspaper. The number of comic strips he creates is represented by the function f(x) = 3x, where f(x) gives the number of comic strips and x is the number of work hours he puts in, which varies day to day. If he puts in {3, 4, 6, 7, 9} work hours, how many comic strips can he write? A. {3, 4, 6, 7, 9} B. {3, 12, 18, 24, 27} C. {9, 12, 18, 21, 27} D. {2, 4, 6, 8, 10}