Maths Question~ 快...

let A be the number of the dogs
the number of hens will be 28-A(coz there are 28 animals)

each dog has 4 legs and each hen has 2 legs
so we have 4A+2(28-A)=68
4A+56-2A=68
2A=12
A=6

there is 6 dogs in the zoo~~

insufficient information