Question

Robbie can clean 72 rooms in 6 days.
How many rooms can Robbie clean in 9 days?

Answer 1

We have a proportional magnitude (directly proportional), if we increase the number of days for cleaning, obviously we will have more rooms cleaned, then:
clean rooms __________ days
72 ----------------------------------- 6
y ------------------------------------- 9
multiply the means by the extremes
Answer:
108 clean rooms in 9 days

Answer 2

108
72/6=12 (unit rate)
12x9=108