To find the amount of oil used, multiply the total amount of oil by the fraction that was used:[tex]$\sf{\frac{2}{4}\times \frac{6}{10} \: liters = \frac{12}{40} \: liters = \frac{3}{10} \: liters}$[/tex][tex]\\[/tex]Final answer:Therefore, [tex]$\sf{\frac{3}{10}}$[/tex] liters of cooking oil was used for frying fish.