Formula help

[Peter]

I need the correct formula for the following propblem...
If(c21=dog then f21+g21) or if (c21=cat then 0,0)

 

[Mike]

=IF(OR(C21="DOG",C21="CAT"),E21+F21,0)

 

[Mike]

Or do you mean this
=IF(C21="DOG",E21+F21,IF(C21="CAT","Zero",0))