Question 364780
Let {{{x}}} = the liters of oj removed from the 2nd tank 
and added to the 1st tank
given:
{{{500 + x = 740 - x}}}
minutes to move {{{x}}} liters from 2nd to 1st tank:
{{{x/20}}}
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{{{2x = 740 - 500}}}
{{{2x = 240}}}
{{{x = 120}}}
minutes to move {{{x}}} liters from 2nd to 1st tank:
{{{x/20}}}
{{{120/20 = 6}}} min
{{{6}}} min x {{{60}}} sec/min = 360 sec