the y-intercept is -3 because that's what y is when x is 0
the slope is 2 because the y-values are going up by 6 every time and the x values are going up by 3. slope is rise/run (rise is y because it's axis is vertical and the run is x because it's axis is horizontal) so the slope is 6/3 or simplified to 2.
to write the equation you plug in the values above into the slope intercept form which is:
The diameter of the circle is equal to 24 yards. The formula to find the circumference of a circle is pi*diameter, so you can work backwards to find your answer.