Let x be the number of minutes they read and y the number of pages they read.
Since Alejandro read one page per minute and he has so far read a total of 28 pages he the total amount of pages he read is:

Now, Carly reads twice as much in the same time but she has read only 12 pages so far, then the amount of pages in her case is:

The graphf of this equations are:
The rate of change:
Alejandro: 1
Carly: 2