I think the answer is D because you have to move the decimal three times anyway, then you only need to add seven more zeroes to make it correct (in my opinion).
V = Bh/3
V = 15 x 28 / 3
V = 420 / 3
V = 140 in^3
Subtract the number she completed from what she had left to paint originally.
The fractions have different denominators so first step is to rewrite the fractions with a common denominator.
23/25 can be rewritten as 92/100
Now you have 78 21/100 - 34 92/100
Because 21/100 is smaller than 92/100 subtract 1 whole number from 78 and rewrite 1 as 100/100 and add that to the fraction.
78 21/100 becomes 77 121/100
Now subtract :
77 121/100 - 34 92/100
77-34 = 43
And 121/100 - 92/100 = 29/100
Combine to get 43 and 29/100
1) subtract 42.5 miles from 68 miles to find the gross change in distance: It is 25.5. Since this is a decrease, write -25.5 miles.
2) divide -25.5 miles by the original distance, 68 miles:
-0.375
3) multiply this by 100% to find the percentage decrease:
-37.5% (answer)