X^2 -144 how do i solve it in difference of perfect squares (Level 1)

Use the function f(x) is graphed below. the graph of the function to find, f(6). -2 -1 1 2

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?

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?