The cool thing about chemical equations is that the mole ratios between compounds is the same as the ratios shown in the balanced equation.
So first, check to make sure the equation is balanced. I just looked at it, and it is (if you can't tell, that means there're the same number of each kind of atom on both sides of the equation).
The answer lies in the coefficients.
So, you'll notice there's a 3 in front of the sodium hydroxide and no coefficient (which implies 1) in front of the iron trichloride.
