$2.80 looks like it is going 20 cents per week
12^3 = 1728 cubes needed.
Since it is volume, and there are 12 inches in one foot, 12 inches will be cubed (to the third power) which gives a total of 1728 cubes needed to fill the cube.
(8/9-3/9)*2/3=5/9*2/3=10/27
Answer:
The answers are, "John saves $35 dollars the first week" and "John is saving at a faster rate than Barb"