A clothing business finds there is a linear relationship between the number of shirts, $n,$ it can sell and the price, $p,$ it can charge per shirt. In particular, historical data shows that $6000$ shirts can be sold at a price of $$67,$ while $10000$ shirts can be sold at a price of $$31.$ Give a linear equation in the form $p=mn+b$ that gives the price $p$ they can charge for $n$ shirts.