She made an error in the STEP 1
she shouldnt multiply the numbers
#13 would be 100%.
#15 would be $9.90.
#17 would be 408.
#19 would be 27840.
#21 would be 26.
Sorry for the late reply.
Answer : There are 13 fish food bags are could fit in a box of size
.
Explanation :
Length of box =
ft
Length of fish food box =
ft
Number of fish food boxes could fit in a box = 
Number of fish food boxes could fit in a box 
Hence, there are 13 fish food bags are could fit in a box of size
.
The answers that you put are right.
Good job!