An observational study.
Explanation:
The researcher randomly makes observation on two groups of 75 people each. He did not interfere with the activity but just assigned the conditions without tampering its effect. Later on he observes and records the effects of each condition on the subjects .Thus, it is a observational study.
The experiment is not a double blinded experiment or a matched pair experiment because the researcher is aware of the conditions applied to the specific subject and their is no pair of subjects made who could be compared for the two conditions.