What is the square root of sixty four

The table respent two linear functions the equation respented by the first tables is given

The parabola opens: y=√x-4 (principal square root) up down right left

Researchers were interested in whether relaxation training decreases the number of headaches a person experiences. they randomly assigned 20 participants to a control group or a relaxation training group and noted the change in number of headaches each group reported from the week before training to the week after training. which statistical analysis should be performed to answer the researchers' question?