12. A manufacturer of college textbooks is interested in estimating the strength of the bindings produced by a particular binding machine. Strength can be measured by recording the force required to pull the pages from the binding. If this force is measured in pounds, how many books should be tested to estimate with 87% confidence to within 0.12 lb, the average force required to break the binding? Assume that s is known to be 0.9 lb. Z = ______ n = _______