An important quality characteristic of water is the concentration of suspended solid material in mg/l. Twelve measurements on suspended solids from a certain lake are as follows: 42.4, 65.7, 29.8, 58.7, 52.1, 55.8, 57.0, 68.7, 67.3, 67.3, 54.3, and 54.0. Calculate the sample average and sample standard deviation. Construct a dot diagram of the data.