Question 746137
The quick guess is 40 liters of each, given numbers like those.


The solving process:

u and v for volumes to use
{{{(15u+25v)/80=20}}} and {{{u+v=80}}}


{{{15u+25v=1600}}}
{{{3u+5v=320}}}

working from volume sum equation, {{{v=80-u}}}, so substitute.
{{{3u+5(80-u)=320}}}
{{{3u+400-5u=320}}}
{{{-2u=320-400}}}
{{{2u=400-320}}}
{{{2u=80}}}
{{{highlight(u=40)}}},   ..... See what I mean?