Respuesta :
Answer:
She will replace both at the same time in 18 months
Step-by-step explanation:
The first thing you have to do to find when she will change them at the same time, is to try with multiples of both, untill they match.
Hall Closet = every 9 months
Air Filter = every 6 months
1) 9-18-27-36-45
2)6-12-18
We find that in the 18th month he will change both of them.