Answer:
18 houses
Step-by-step explanation:
First, find out how many houses they can clean in 1 hour.
10/5=2
They can clean 2 houses in 1 hour.
With this information, you can now multiply the number of houses in 1 hour by 9 hours to find out how many houses are cleaned in 9 hours.
9*2=18
Therefore they can clean 18 houses in 9 hours.