So if Jenny can type 1,200 words in 15 minutes, and its asking how many she can type in an hour, lets see, 15 goes into 60 4 times right?
So you are going to multiply 1,200 by 4.
1,200 x 4 = 4,800
To check your work you can divide
4,800 / 4 = 1,200
Hope this helped!