An investigator is studying the effects of expansions on the mean length of utterances of young children. Spontaneous language samples are obtained from forty-six two and three year olds both prior to and following therapeutic intervention. The sole method of treatment is for the clinician to follow the child's lead, and expand any utterances produced by the child. At the completion of three months of therapy, a post-treatment MLU is calculated. The groups mean pre-therapy MLU was 3.6 while the mean post- therapy MLU was 4.8, with a pooled standard deviation of 1.5. a. Using only data from these 46 children, what is the statistical power? b. How many more children must be added to each group to produce a power of .80