creating an equation

Question

 

 mrs custer has 100 bushels of soybeans to sell. The current price for soybeans is $6.00 a bushel. She expects the market price of a bushel to rise in the coming weeks at a rate of $0.10 per week. For each week she wait to sell, she loses 1 bushel due to spoilage. Find a function to express Mrs.Custers total income from selling the soybeans. Graph the function and determine when Mrs.Custer should sell the soybeans in order to maximize her income. Justify your answer by showing that selling a short time earlier or a short time later would result in less income.