Your first conversion is converting grams NaOH to moles of NaOH using its molar mass (39.997 g/mol). Then, use the mole ratio of 1 mol NaCl for every 1 mol NaOH to get to moles of NaCl. Then finally multiply by the molar mass of NaCl (58.44 g/mol) to get grams of NaCl.
20.6 g NaOH • (1 mol NaOH / 39.997 g NaOH) • (1 mol NaCl / 1 mol NaOH) • (58.44 g NaCl / 1 mol NaCl) = 30.1 g NaCl
