You have to use the substitution method by substituting one Y value with the other
11: 4,874 > 4,784 > 4,687
12: 8.09 > 8.057 > 8.023
13: 15.820 > 15.280 > 15.000
14: 43,628 > 40,628 > 34,628
15: 395.050 > 395.009 > 395.005
Answer:
The equation for a is 
The altitute is 101,428.57 feet
Step-by-step explanation:
You know that the relationship between ground temperature and atmospheric temperature can be described by the formula
t = -0.0035a +g
where:
- t is the atmospheric temperature in degrees Fahrenheit
- a is the altitude, in feet, at which the atmospheric temperature is measured
- g is the ground temperature in degrees Fahrenheit.
Solving the equation for a:
-0.0035a +g=t
-0.0035a= t - g


<u><em>The equation for a is </em></u>
<u><em></em></u>
If the atmospheric temperature is -305 °F and the ground temperature is 50 °F, then t= -305 °F and g= 50 °F
Replacing in the equation for a you get:


a= 101,428.57
<u><em>The altitute is 101,428.57 feet</em></u>