Consider the question below.

If 9 mole of NaNO₃ are formed how many mole of NaCl were used up?

Lets start with 9 mole of NaNO₃ . Looking at the equation we see that the ratio of NaCl used and NaNO₃ produced is 3 : 3 or 1 : 1. We therefore conclude that we used 9 mole of NaCl.