68% nitric acid by mass means that

Mass of nitric acid = 68 g

Mass of solution = 100 g

Molar mass of HNO_{3} = 63 g mol^{-1}

68 g HNO_{3} = mole = 1.079 mole

Density of solution = 1.504 g mL^{-1}

Volume of solution = \(\frac{100}{1.504}\) mL = 66.5 mL = 0.0665 L