Question 1160521
v, amount of the 90% alcohol to use
150-v, amount of the 80% alcohol to use


Accounting for the amount of pure alcohol
{{{90v+55(150-v)=80*150}}}

-

{{{90v-55v+55*150=80*150}}}

{{{(90-55)v=80*150-55*150}}}

.

.
{{{highlight_green(v=150((80-55)/(90-55)))}}}

.