The answer to the question is "B. Roman Numerals"
The coefficients of the substances give you the ratio of the number of moles.
The 4 before the H2O and the 5 before the HCl tell you that for every 5 moles of HCl created, 4 moles of H2O had to react.
Therefore:

can be used to find the moles of H2O that react.
The answer would be D, all the above
The answer is 5 if u multiple