Confidence Intervals question

I know how to use my calculator to actually find a confidence interval, but I don't know how to work backwards if you are given the C.I. and asked to find other information.

Here is my sample:
23, 67, 45, 45, 35, 46, 39, 67, 38, 51, 37, 44, 56, 46, 40

This is what I have already calculated:
mean: 45.5667
std. deviation: 11.6034

The question I don't know how to answer:
What is the confidence level for the confidence interval shown below? (37.4037, 53.1296).

Do you have a textbook? You need to know the formula for a (normal) confidence interval (for a population mean), and a little algebra.