You can do a Cartesian plane graph your points can be (65,58) and (72,86) the dependent variable (chirping) is always y point, the slope formula gives us 86-56/72-65 which simplifies to 30/7 which is our slope, then we plug in one of the points, 30/7(65)+b=58, which simplifies to b=-649.14 the equation is 30/7x-649.14=y