a dozen is 12, so 3 dozens is 3 times 12, that is 36.
so we know how much of baking powder do we need for 8, and we want to know how much we will need for 36 muffins.
this will be [tex] \frac{36}{8}= \frac{18}{4}= \frac{9}{2}=4.5 [/tex] times more
so we will need 4.5 times more baking powder than for eight ( I think you forgot to say how much you needed for 8, but you can just multiply this number by 4.5
