"Seo dà chù."
Translation:These are two dogs.
Two separate things going on here.
Dà is one of those words that causes lenition (insertion of the h after most consonants).
As a completely different matter you use the singular after the word dà. The reasons are not important - it's just one of those things - but if you want to know see here: https://forum.duolingo.com/comment/35499193?comment_id=37609255
The plural of cù is in fact coin. Slightly odd but discussed here: https://forum.duolingo.com/comment/37316387?comment_id=37643691