Research has shown that people are more likely to show dishonest and self-interested behaviors in darkness than

Question:

Research has shown that people are more likely to show dishonest and self-interested behaviors in darkness than in a well-lit environment (Zhong, Bohns, & Gino, 2010). In one experiment, participants were given a set of 20 puzzles and were paid $0.50 for each one solved in a 5-minute period. However, the participants reported their own performance and there was no obvious method for checking their honesty.
Thus, the task provided a clear opportunity to cheat and receive undeserved money. One group of participants was tested in a room with dimmed lighting and a second group was tested in a well-lit room. The reported number of solved puzzles was recorded for each individual. The following data represent results similar to those obtained in the study.

a. Is there a significant difference in reported performance between the two conditions? Use a two tailed test with a = .01.
b. Compute Cohen's d to estimate the size of the treatment effect.