Six different types of acids are used in removing film from a machine part. A plant manager wants to test which acid removes the film in the least amount of time. Forty two machine parts are chosen, and each acid is used on seven different parts. The time it takes to remove the film is measured for each of the forty two parts. (a) Is this an observational study or an experiment? Explain why or why not. (b) If it is an experiment, give the treatments, experimental unit, and response variable.