Since they tell us that this is linear, having a constant rate of change, we can express this as a line:
y=mx+b, where m=slope (change in y divided by change in x) and b=y-intercept (value of y when x=0)
First find the slope, or m, which mathematically is:
m=(y2-y1)/(x2-x1), in this case:
m=(880-440)/(2000-1000)
m=440/1000
m=0.44, so far our line is:
y=0.44x+b, now we can use either data point to solve for b, I'll use (1000,440)
440=0.44(1000)+b
440=440+b
0=b, so our line is just:
y=0.44x
