Confusing statistics question using CLT...can some one help?

I'm going to assume you have access to a t table. Because it sounds like you are comparing one sample to a hypothetical population, you would use a degrees of freedom of n-1, not n-2. If you are comparing two independent samples to each other, then your degrees of freedom would be n-2. Because your p-value is .02, that means there is .01 in each tail. If you look at the t table, find the row for the correct degrees of freedom (n-1=20-1=19) and the correct column for either p=.01, one tailed, or p=.02, two tailed, depending on how the table you have is set up. The value that you get will be the test statistic in terms of a t value. If you have the mean and standard deviation from the sample, you can transform that back into the observed scale.