Roberto wants to display his 18 sports cards in an album. some pages hold 2 cards and others hold 3 cards. how many different ways can roberto display his figures?

Assuming Roberto wants to completely fill each page that he puts cards in, this function describes the number of 2-card pages, a, and 3-card pages, b.
2a + 3b =18
Ricardo can fill up 9 2-card pages, and 6 3-card pages.
a=9, b=0
We must add 2 3-card pages at a time,so that we have an even number for the 2-card pages:
a=6, b=2
Add 2 to b once more:
a=3, b=4
One more time:
a=0, b=6:
Thus, Ricardo can display his figures in the following page combinations:
a=9, b=0
a=6, b=2
a=3, b=4
a=0, b=6
Remember that a= number of 2-card pages and b=number of 3-card pages

There are 4 different ways that Ricardo can arrange his figures in terms of what kind of pages he uses.