Hey there!
Since she mows 1/4 in 3/4 hours, you can multiply 4 and 3/4 . . .
4 = 4/1
3/4 = 3/4
4 x 3 = 12
1 x 4 = 4
Simplifying 12/4 . . .
12/4 = 3 <---------
It will take 3 hours for Cheryl to mow the entire lawn.
Hope this helps you.
Have a great day!