A random sample of 40 farming regions gave a sample mean of $6.88 per 100 pounds of watermelon. Assume that standard deviation is known to be $1.90 per 100 pounds. Find a 90% confidence interval for...

A random sample of 40 farming regions gave a sample mean of $6.88 per 100 pounds of watermelon. Assume that standard deviation is known to be $1.90 per 100 pounds. Find a 90% confidence interval for the population mean price that farmers in this region get for their watermelon crop. Find the sample size necessary for a 90% confidence level with maximal error of 0.39 for mean price. A farm brings 15 tons of watermelon to the market. Find 90% confidence interval for the population mean cash value of this crop. What is the margin of error