Question 889725
1.{{{A=S+20}}}
In ten years,
{{{A+10=2(S+10)}}}
{{{A+10=2S+20}}}
2.{{{A-2S=10}}}
Substituting from eq. 1,
{{{(S+20)-2S=10}}}
{{{-S+20=10}}}
{{{-S=-10}}}
{{{S=10}}}
Then,
{{{A=10+20}}}
{{{A=30}}}