First, write the chemical reaction and balance it:
NBr3 + NaOH ---> N2 + NaBr + HOBr
2 NBr3 + 3 NaOH ---> N2 + 3 NaBr + 3 HOBr
Then the theoretical proportion is 2 NBr3 : 3 NaOH
The reactants are in the proportion 40 NBr : 48 NaOH
From the theoretical proportion you can make [2 NBr3 / 3 NaOH] * 48 NaOH = 32 NaOH.
Given that you have more than 32 moles of NaOH, this is the excess reactant.
