The equation shows the relationship between a planet’s orbital period, t, and the planet’s mean distance from the sun, a, in astronomical units, au. if planet y is k times the mean distance from the sun as planet x, by what factor is the orbital period increased?

Basically, this deals with Kepler's Third Law: T^2 = r^3
Let's suppose Planet Y is twice as distant as Planet X.
So, if we increase the distance by a factor of "k", then "r" becomes:
2^2 = r^3
r = cube root (4)
r = 1.587401052

Source:
http://www.1728.org/kepler3a.htm

Abit confused about what you mean, but i think you might be referring to slope intercept form: y = mx + bin that case b, or the y intercept is already given.(0,-1)find the slope by using the formulay2 - y1/x2 - x1the final slope will be 4/2, equivalent to 2.now your equation should look like thisy = 4/2x -1sorry if this didn’t you out!