How do I get past level 18 in alpha Betty

marchn_2_my_drum

There seems to be no rhyme or reason to the outside 5 bubbles.  Do they clear just on luck?  I have cleared 4 of the 5 but wasn't able to actually discern how I did it  

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StuckInATree

When you make 4 letter words you will be rewarded with a little crown on a tile, when you use this tile when making a word, it will go off and pop one of those bubbles, that's how you pop them!