Question 765417
The basic unit used is ml, for volume.  

Let V=volume in ml, unknown.


{{{(1/3)V}}} is the volume in ml, of the orange juice.
{{{(1/3)V+20+40=V}}} is the accounting for volumes.
Multiply left side and right side by 3 and continue steps to solve for V.


{{{V+60+120=3V}}}
{{{0+180=2V}}}
{{{highlight(V=90)}}}