Business Statistics: Sampling Error

This is a question I had on my exam and got wrong: Can someone please do step by step so I can follow along:

The right answer is:

Sampling Error=5.24-7.4=-2.16

The sample mean is 2.16 lower then the population mean of 7.4

The Question:

An investment advisor has worked with 24 clients for the past five years. Following are the percentage rates of average five-year returns that these 24 clients have experienced over this time frame on their investment:

11.2, 11.2, 15.9, 2.7, 4.6, 7.6, 15.6, 1.3, 3.3, 4.8, 12.8, 14.9, 10.1, 10.9, 4.9, -2.1, 12.5, 3.7, 7.6, 4.9, 10.2, 0.4, 9.6, -0.5

I got the mean right which was 7.4

This investment advisor plans to produce a new investment program to a sample of his customers this year. Because this is experimental, he plans to randomly select 5 of the customers to be part of the program. However, he would like those selected to have a mean return rate close to the population mean for the 24 clients. Suppose the following five values represent the average five-year annual return for the clients that were selected in the random sample:

11.2, -2.1, 12.5, 1.3, 3.3

Calculate the sampling error associated with the mean of this random sample. What would you tell this advisor regarding the sample he has selected?