-Cindy plans to sell her car and she wants to get $8000 for it. She knows
that if a buyer makes an offer of a and she makes a counter-offer of b and if
they negotiate back and forth, going exactly half way each time, the final
price they settle on will be a+2b/3
If someone offers her $6000, what
should her counter-offer be, so that they settle on the $8000 that she wants?