Here are the things we know about this problem:

Model A can print 80 books per day and Model B can print 60 books per day. (We will use "A" to represent Model A and "B" to represent Model B)

The total number of books printed, or "jobs", is 1260.

There are 18 printing presses.

Using this information, we can come up with an equation.

(80/1)(A) + (60/1)(B) = 1260

...There are two variables that we don't know. But, we do know that there are 18 total printing presses, so we can represent the variable B as (18 - A):

(80)(A) + (60)(18-A) = 1260

Now we just do the math.

(80A) + (-60A + 1080) = 1260

A = 9

Now we can go back and substitute A back in (18 - A) to find B.

18 - 9 = 9, B = 9

I haven't done these rate problems in a while so there's room for mistake, so please correct me if I'm wrong