Respuesta :

Americ
This is a proportion problem. 2 1/4 cups is to 8 muffins as x is to 13 muffins.

2.25/8=x/13
Cross multiply
(2.25*13)=(8*x)
29.25=8x
Divide both sides by 8
3.65= x
x=3.65 cups of flour

Hope this helps! :)