Answer
Find out the how long does it take to install one sheet of drywall .
To prove
As given
A carpenter can install 8 sheets of drywall in 10 minutes.
8 sheets = 10 mintues
Now


Time taken for installing one sheets of drywall = 1.25 mintues.
Now Find out how long will it take the carpenter to install 60 sheets .
To prove
As given
A carpenter can install 8 sheets of drywall in 10 minutes.
8 sheets = 10 mintues

Now for 60 sheets.



As 1 hour = 60 mintues

Now convert 75 mintues into the hours.

Time taken for installing 60 sheets = 1.25 hours.
Therefore the option (A) is correct.
Thus 1.25 minutes take to install one sheet of drywall and 1.25 hours take the carpenter to install 60 sheets .