50. The dosage of a cold medication is 2 mg for every 80 lb of body weight. How many milligrams of this medication are required for a person who weighs 220 lb?

51. A credit card company offers an annual 2% cash-back rebate on all gasoline purchases. If a family spent $6850 on gasoline purchases over the course of a year, what was the family's rebate at the end of the year ?

52. In a recent year, wind machines in a country generated 189.1 billion kWh of electricity, enough to serve over 15 million households. The nation's total electricity production that year was 4,092 billion kWh. What percent of the total energy production was generated by wind machines? Round to the nearest tenth of a percent.

54. The area A, in square meters, of a rectangle with a perimeter of 140 meters is given by the equation A = 70w w², where w is the width of the rectangle in meters. What is the width of a rectangle if its area is 600 m² ?

56. A couple plans to save for their child's college education. What principal must be deposited by the parents when their child is born in order to have $42,000 when the child reaches the age of 18? Assume the money earns 9% interest, compounded quarterly. (Round your answer to two decimal places.)