Don't understand can you explain please! I need the help

The shape of the distribution of the time required to get an oil change at a 20minute oilchange facility is unknown. However, records indicate that the mean time is 21.2 minutes, and the standard deviation is 4.7 minutes. (a) To compute probabilities regarding the sample mean using the normal model, what size sample would be required? (b) What is the probability that a random sample of n = 35 oil changes results in a sample mean time less than 20 minutes? (a) Choose the required sample size below. 0 A. 'he normal model cannot be used ifthe shape of the distribution is unknown. 0 B. "he sample size needs to be greater than 30. O C. Any sample size could be used. 0 D. "he sample size needs to be less than 30. (b) The probability is approximately |:. (Round 0 four decimal places as needed.) 1) B 2) 0.0655 Part A solution is from the definition of Central Limit Theory so nothing to explain Part B: Required probability = (