18. Schadek Silkscreen Printing Inc. purchases plastic cups and imprints them with logos for sporting events, proms, birthdays, and other special occasions. Zack Schadek, the owner, received a large shipment this morning. To ensure the quality of the shipment, he selected a random sample of 300 cups and inspected them for defects. He found 15 to be defective. a. What is the estimated proportion defective in the population? b. Develop a 95% confidence interval for the proportion defective. c. Zack has an agreement with his supplier that if 10% or more of the cups are defective, he can return the order. Should he return this lot? Explain your decision