How many grams of naoh must be used to make 500. ml of a 6.00 m solution?

Remember the units of M (molarity) is the number of moles per liter (mol/L).
First, convert mL to L:
500. mL * (1 L / 1000 mL) = 0.500 L
Convert Molarity into moles by multiplying by the volume:
6.00 (moles/Liter) * (0.500 Liters) = 3.00 moles NaOH
Finally, multiply the number of moles of NaOH by the molar mass:
Molar mass = (22.99 g/mol) + (16.00 g/mol) + (1.01 g/mol) = 40.00 g/mol
3.00 moles * (40.00 grams/mole) = 1.20 * 10^2 grams