d : c = 33 : 22
where d is the number of dogs and c is the number of cats;
and: d + c = 3030
33 c = 22 d / : 11
3 c = 2 d
From the other equation: c = 3030 - d
3 * ( 3030 - d ) = 2 d
9090 - 3 d = 2 d
5 d = 9090
d = 9090 : 5
d = 1818
Answer: There are 1818 dogs in the shelter.
