Let T be the time that is needed for a specific task in a factory to be completed. In order to estimate the mean and variance of T, we observe a random sample T₁,T₂,⋯, T₆. Thus, T_i's are i.i.d. and have the same distribution as T. We obtain the following values (in minutes): 18, 21, 17, 16, 24, 20. Find the values of the sample mean, the sample variance, and the sample standard deviation for the observed sample.