Sentences like 'how do you like it' usually don't really translate with tycka om, rather we'd say hur vill du ha det 'how do you want it' or something like that. Depending on what's actually meant by the sentence of course, but usually 'how do you like it' doesn't literally mean 'how do you like it'.
Because det does not replace the object (en myra, in this case), it's just a functor (which means that it makes it possible that en myra takes the objects place in the sentence, otherwise you would have to say en myra är, which isn't useful at all) Actually if it would replace the noun you'd also say "en myra är en myra". But with using det it means that "a specific object"(which isn't defined yet) är en myra.
So you only use "den" as an object pronoun when den replaces the noun
The voice is not quite perfect on this sentence, as of May 10th, 2018, so I've taken the liberty of re-recording it.
In this case, the error isn't huge. But tycker om is a so-called particle verb in Swedish, meaning that it's one verb consisting of multiple words. If you leave either word out, the meaning usually changes completely. And hence, stressing the right word is important. Almost always, this means putting the stress on the particle - the om, in this case. The automatically generated voice has a tendency to put the stress on tycker instead, which is never correct, or on the word after tycker om.
Please find a correct recording on http://duolingo.vydea.io/a36a7debb1654218b6d08e0f929d1988.mp3
For more info on re-recordings, please check the info thread: https://www.duolingo.com/comment/23723515
Thanks for listening. Ha en bra dag! :)
https://youtu.be/avoKDIEyJ6M?t=49s Are you a native? Just wondering. I'm just really confused and I want to believe you and I know it's a baby, but I just wanna be completely sure. Also I kinda like the idea of "Jag tycker det om" it's really cool. But if you're sure that's fine. Sorry to bother.