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Will someone please help me with these statistics word problems?

A business wants to estimate the true mean annual income of its customers. It randomly samples 200 of its customers. The mean annual income was $55,200 with a standard deviation of $1,500. Find a 95% confidence interval for the true mean annual income of the business’ customers. A business wants to estimate the true mean annual income of its customers. The business needs to be within $200 of the true mean. The business estimates the true population standard deviation is around $1,300. If the confidence level is 95%, find the required sample size in order to meet the desired accuracy. An automobile safety engineer wants to estimate the mean cost to repair a Chevy Corvette involved in a 30 mile per hour head-on collision. The engineer crashes 18 Corvettes and finds the mean damage is $17,500 with a standard deviation of $2,400. Find a 95% confidence interval for the true mean cost to repair this type of car. An auditor wants to estimate what proportion of a bank’s commercial loan files are incomplete. The auditor wants to be within 7% of the true proportion when using a 95% confidence level. How many files must the auditor sample? No estimate of the proportion is available, so use 0.5 for the population proportion.

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1. this site should help you: http://www.dimensionresearch.com/resources/calculators/conf_means.html
2. A) The confidence interval is found by: Xbar ± Zα/2(σ/√n) Evaluating, 55200 ± 1.96(1500/√200) And the interval is: 54992.11 < µ < 55407.89 B) n = [1.96∙1300/200]² ≈ 163 C) You do this one like (A) above. D) This one id different from (B) because it uses proportions. n = [Zα/2/E]²(p(1-p)) = [1.96/0.07]²(0.50)(.0.50) = 196 exactly