Answer:
or 
Step-by-step explanation:
To find a fraction of a fraction simply multiply the numerators and denominators into another fraction:

Answer:
A = 49 ft^2
Step-by-step explanation:
The perimeter of a square is given by
P = 4s where s is the side length
28 = 4s
Divide each side by 4
28/4 = 4s/4
7 =s
We want the area
A = s^2
A = 7^2
A = 49 ft^2
He should use an average of 20%, and I'm assuming, since not enough info is given, that 1 gallon of milk has the given stats. The average of 20% would mean that he needs to have a 2/3 ratio of 18 to 24, because 18:24 = 6:8, which equals 2:3, so, therefore, he needs to have 42/5 = 8.4, then 8.4*2, 9.4*3 = 16.8 and 28.2, respectively, and if you add those, you get 42.
Hope this helps and have a nice day:)