The average electric bill in a residential area is $72 for the month of April. The standard deviation is $6. If the amounts of the electric bills are normally distributed, find the probability that

(a) the amount of bill (X) for a randomly selected resident will be less than $74;

(b) the mean amount ( X) of the bill for a random sample of 36 residents will be less than $74.

Hand written answer. I will rate accordingly. Solve it correctly please. My last attempt...