Answer:
Number 11: She has to add 5/36 of a cup
Number 12: The present costs $22,2
Number 13: 56,7 pounds is the weight of the package.
Number 14: You started with 40 muffins
Explanation:
Number 11: 1/4 = 9/36 and 1/9 = 4/36
3*1/4 - 3*1/9 = 3*9/36 - 3*4/36 = 5/36
Number 12: 13,32/x= 3/5 ( or 0,6)
x = 13,32/0,6 = 22,2
Number 13: x * 5/7 = 40,5
x = 40,5/ (5/7) or 40,5 * 7/5 = 283,5/5 = 56,7
Number 14: 12/x = 3/10 (or 0,30)
x= 12/0,30 = 40