Question 1184622
This has already been answered, more than once.
Elimination Method for this is very uncomplicated.



{{{system(3A+5B=9,12A+2B=9)}}}


{{{system(4(3A+5B)=4*9,12A+2B=9)}}}


{{{system(12A+20B=36,12A+2B=9)}}}


{{{E1-E2}}}
{{{(12A+20B)-(12A+2B)=36-9}}}
{{{18B=27}}}
{{{2B=3}}}
{{{highlight(B=1&1/2)}}}-------------hours for one session of plan B.



And you should know how to find A.