Question 611414
Let's write this mathematically. We'll represent age by x.
Mark is 11 years older than his sister (11+x). In eight years (+8) he will be twice as old as his sister (2x).
So, it'd be: {{{2x+8=11+x}}}
Let's simplify that: {{{simplify_cartoon( 2*x+8=11+x )}}}
Now we know that x=3, so we plug it back into the original formula: {{{11+3}}}, so Mark is 14 and his sister is 3. :)