Answer:
Option B. is correct
Step-by-step explanation:
Let [tex]x[/tex] denotes time taken by Mia alone to clean the room and [tex]y[/tex] denotes time taken by Holly alone to clean the room.
As Mia and Holly can clean their room in 20 min, working together,
[tex]\frac{1}{x}+\frac{1}{y} =\frac{1}{20}\,\,\,...(i)[/tex]
Also,
Mia, working alone, can do the job in 30 min.
So,
[tex]\frac{1}{x}=\frac{1}{30}\,\,\,\,\,...(ii)[/tex]
Put (ii) in (i)
[tex]\frac{1}{30}+\frac{1}{y}=\frac{1}{20}\\\frac{1}{y}=\frac{1}{20}-\frac{1}{30}\\\frac{1}{y}=\frac{3-2}{60} \\\frac{1}{y}=\frac{1}{60}[/tex]
Therefore,
Holly can clean the room alone in 60 minutes.
Option B. is correct
