Equation of straight line y = mx+b
Where x and y are the coordinates of X-axis and Y-axis respectively
m = slope of line
And b = y-inercept (when x= 0)
We know temperature is a function of altitude.
So taking altitude at X-axis and temperature at Y-axis
When altitude (x) = 0
Temperature = 59
So b = 59
We know m = Y2-Y1/X2-X1
43-51/4000-2000 = -8/2000
m = -1/250
By putting the values of m and b in general equation of line,
y = (-1/250)x+59