6.75 teaspoons
So it takes 0.1875 teaspoon of baking powder to make one muffin. Then you just multiply 0.1875 by 36 and you get 6.75. :)
If you need to simplify the equation it would be:

+2r-2n+7
If not sorry..
Hope This Helps!
I believe it's C.
(Hint: y=mx+b)
M is Slope and B is Y-Intercept.