Two different types of injection-molding machines are used to form plastic parts. A part is considered defective if it has excessive shrinkage or is discolored. Two random samples, each of size 300, are selected, and 12 defective parts are found in the sample from machine 1 whereas 10 defective parts are found in the sample from machine 2. Construct a 95% CI on the difference in the two fractions defective.