Answer:
the formula for a straight line is y=mx+b where m is your slope (so 2 in this case) and b is your y-intercept (your initial value is what I think they call it here)
Explanation:
I already explained this in the "ask [insert name here] about this question" thing, but out of the goodness of my heart I can do it once more. Just take random 2 coordinates and take the difference of the y values and divide it by the difference of the 2 x coordinates. Simple! Any more questions just ask me on this or DM me