4. We would like to estimate the true mean annual electricity usage by all Canadian homes. Suppose that annual electricity usage follows a normal distribution with standard devi- ation 1499 kilowatt hours (kWh). (a) What sample size is required to estimate the true mean annual electricity usage to within 400 kWh with 95% confidence? (b) What sample size is required to estimate the true mean annual electricity usage to within 100 kWh with 95% confidence? (c) For a given confidence level, how many times larger a sample size is required when we divide the desired margin of error by four