The osmotic pressure exerted by a solution is equal to the molarity multiplied by the absolute temperature and the gas constant $R.$ Suppose the osmotic pressure of a certain solution is measured to be $20.$ atm at an absolute temperature of $391.$ K$.$

Write an equation that will let you calculate the molarity $c$ of this solution. Your equation should contain only symbols. Be sure you define each symbol other than $R.$

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