20 ml solution containing mixture of NaOH and Na2CO3  require 60 ml of 0.5 N  H2SO4 for the end point using phenolphthalein as indicator. After this when same solution was titrated using methyl orange indicator. A further 20 ml of 0.5 N  H2SO4 was needed for the second end point. Calculate the molarity of NaOH.