first we make 2 equations from the given info
let c = cats & b = birds
[tex]c + b = 11[/tex]
[tex]4c + 2b = 36[/tex]
^ because cats have 4 legs and birds have 2
now next we want to solve for one of the variable in the first equation, then plug it into the second one
so..
[tex]b = 11 - c[/tex]
now plug it in
[tex]4c + 22 - 2c = 36[/tex]
simplify
[tex]2c = 14[/tex]
[tex]c = 7[/tex]
now all we have to do is put 7 back into our first equation
[tex]7 + b = 11[/tex]
[tex]b = 4[/tex]
7 cats
4 birds
