well to help you solve this problem you should set an equation as so...
B=5F
B+F=120
Next you would plug in what B equals into the equation B+F=120 like so
5F+F=120
then you add like terms
6F=120
then you isolate the variable by dividing like so
6F=120
F=20
so Allison has 20 football cards and you would subtract 20 from 120
120-20=100
so Allison has 100 baseball cards