5.Economists define the disposable annual income for an individual by the equation D = (1 - r) T, where T is the individual's total income and r is the net rate at which he or she is taxed. What is the disposable income for an individual whose income is $70,000 and whose net tax rate is 25%?

6.An apple orchard has an average yield of 36 bushels of apples/tree if tree density is 24 trees/acre. For each unit increase in tree density, the yield decreases by 3 bushels. Letting x denote the number of trees beyond 24/acre, find a function in x that gives the yield of apples.

7.The owner of a luxury motor yacht that sails among the 4,000 Greek islands charges $800.00/person/day if exactly 20 people sign up for the cruise. However, if more than 20 people sign up (up to the maximum capacity of 90) for the cruise, then each fare is reduced by $3.00 for each additional passenger. Assume at least 20 people sign up for the cruise and let x denote the number of passengers above 20. Find a function R giving the revenue/day realized from the charter.