1.
What do you know?
the troposphere extends 8 to 20 km above the Earth's surface. The surface temperature is 15°C and decreases at a rate of 6.5°C per kilometer away.
What do you want to find out?
The temperature at any point of the troposphere
What kind of answer do you expect?
Any value below 15°C
2. Define variables,
T is for temperature, and
d is the distance away from the surface
3. What is the b -value
b = 15
which is the Earth's surface temperature or the initial temperature for our problem
4. What is the slope
the slope 'm' equals -6.5
which means that the temperature decreases 6.5°C per km
5. write the equation

the general form for this equations is y = b + mx
thus, for our problem, the equation is: T = 15 - 6.5*d
6.
a) the slope represents the rate of change of temperature with respect to distance, since m = -6.5 °C/km , this means the troposphere is getting 6.5 °C colder per km away from Earth's surface
b) the y-intercept represents the Earth's surface temperature
Graph:
7. identify 3 points
when d = 0 then T = 15, so our first point is (0,15)
when d = 1 then T = 15 - 6.5 = 8.5 , so our second point is (1,8.5)
when d = 2 then T = 15 - 13 = 2 so our third point is (2,2)
8. calculate the slope
let's use this equation and this set of points,

let's replace and solve

We can see that it does match the slope from our model, which is -6.5
9. graph the line and the points,
10. Complete the sentence
... ends between 8 km and 20 km above Earth.
11. temperature at the farthest point
when d = 20 then,

... the temperature is -115°C
12. Temperature range,
from... 15 °C to -115 °C