11-8. Suppose we wish to estimate the average daily yield (in terms of telephone inquiries) of a new magazine ad for a certain product. We want a degree of precision of ±3 telephone calls with 95% reliability. If it is known that σ = 10 calls, find the required sample size. If σ is unknown but evidence indicates that the calls are approximately normally distributed with a range of about 60 calls, recalculate n.