If I go 14-16. 2. Can I take 30 days from Ranong to Kawthaung and back? Yep I am from Finland. Thank U :)

If you mean can you get a 30-day visa exempt entry the answer is yes. 

I think your question is 'can I go from Ranong to Kawthaung on 14 Feb, stay two nights, and then return to Ranong receiving a 30-day visa exempt entry?' This is possible, yes. I believe you can get a seven-day border pass for Kawthaung on arrival, but this does not allow you to travel far outside the town. Almost no one does that. Most get either a same-day border pass for quick in/out visa runs.; or, if you want to do a lot of sightseeing, you should get a Myanmar eVisa in advance. On your return to Thailand, you will get your visa exempt entry, but this counts as an entry by land. You are only allowed two visa exempt entries when entering by land in any calendar year. If you are planning to hang around in Thailand for a significant period, husband you land based visa exempt entries. They are valuable for emergencies.

Ok, Thank You, last time Burma, Kawthaung give me 14 days, April 2018. 10USD. But yep I do only visa exempt entry. I have so many Tourist visa and April I take new passport.