Mr. Jones and Mr. Smith occupy adjacent beds in the ICU. Smith needs his IV changed every 15 hours. Jones needs his IV changed every 9 hours. The nurse changes both IVs together when a 12-hour clock reads 3:00. What does that clock read the next time the nurse changes IVs together?
a. 9:00
b. 12:00
c. 3:00
d. 6:00