A survey of 39 randomly selected "iPhone" owners showed that the purchase pricehas a mean of $403 with a sample standard deviation of $160.

a.Compute the standard error of the sample mean.(Round the final answer to the nearest whole number.)

Standard error= 26

b.Compute the 95% confidence interval for the mean.(Round the final answers to 2 decimal places.)

The confidence interval is between $351.13and $454.87.

c.How large a sample is needed to estimate the population mean within $11 at a 95% degree of confidence?(Round the final answer to the nearest whole number.)

Sample size______?