A real estate agent agrees to sell an apartment complex according to the following commission​ schedule: ​$50,000 plus 20​% of the selling price in excess of ​$850,000. Assuming that the complex will sell at some price between ​$850,000and ​$1,200,000 ​inclusive, over what range does the​ agent's commission​ vary? How does the commission vary as a percent of selling​ price?