Two machines, y and z, work at constant rates producing identical items. machine y produces 3 items in the same time machine z produces 2 items. if machine y takes 9 minutes to produce a batch of items, how many minutes does it take for machine z to produce the same number of items?

a. 6
b. 9
c. 9 1/2
d. 12
e. 13 1/2