Example 1: A compound is formed by a chemical reaction . The mass , M , in grams , of the 8.5 t compound is modelled by M (t)=. t + 4.1 where t is the time after the start of the reaction , in seconds a) Determine the rate of change of the mass after 5 seconds b) Is the rate of change of the mass ever negative ? Explain Example 2: A bakery sells 350 fruit tarts each month for $3.25 each . The results of a survey indicate that sales of fruit tarts would increase by 80 per month for each $0.10 decrease in price a) Determine the demand function b) Determine the revenue and marginal revenue from the monthly sales of 200 fruit tarts