In this question, we have to find out how many grams of NaOH are in 3 moles of this compound, and the way to do that is by using its molar mass, 40g/mol, which means that in 1 mol of NaOH, we will have 40 grams, therefore, in 3 moles:
40g = 1 mol of NaOH
x grams = 3 moles of NaOH
x = 3 * 40
x = 120 grams of NaOH in 3 moles