It's C, I'm learning about the same thing in math right now.
Yesterday on a math quiz, I had a problem almost exactly the same as this one. The only difference was the numbers were swapped so instead of heads being 84 it was tails and the amount of heads was 66.
Hope this helps!! :-)
I would go with C because it would more than likely be the same answer but i'm not fully sure, but still go with it. :-)
