the answer is c, 56. first you would subtract the amount of water that remains from the original, total amount to get the amount of water that was used.
16-7=9
then you would take 9 and divide it by 16 to get the percentage of the total amount that was used.
9/16= .5625
then you would take the decimal and convert it into a percentage.
.5625= 56.25%
i hope this helps!!