Question 1185489
I took the description as a step-wise process, not as two separate conditions.
<pre>
             Arthur          Sam

   0          A               S

   1          A-20            S+20

   2          A-20+10         S+20-10
</pre>

Description makes these relations.
{{{system(A-20=S+20,(A-10)/(S+10)=2)}}}


Some algebra steps,


{{{system(A-S=40,A-10=2S+20)}}}


{{{system(A-S=40,A-2S=30)}}}
Solve this system for S and A.



************************************THIS IS WHAT YOU'RE LOOKING FOR*******************************************


As two separate conditions,

{{{system(A-20=S+20,(A+10)/(S-10)=2)}}}


{{{system(A-S=40,A+10=2S-20)}}}


{{{system(A-S=40,A-2S=-30)}}}


{{{system(A-S=40,-A+2S=30)}}}


Add them;
{{{highlight(S=70)}}}

and {{{A-S=40}}}
{{{A=40+S}}}
{{{A=40+70}}}
{{{highlight(A=110)}}}