Answer for the first box: 38
Answer for the second box: -3
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Explanations:
To get the first answer, you plug in x = 0 to reflect were at the surface (height is 0)
38-3x = y
y = -3x+38
y = -3*0+38
y = 38
So the temperature at the surface is 38 degrees Celsius
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Each time x increases by 1 km, y decreases by 3 degrees C. How do we know? Because of the slope m = -3
Note how y = -3x+38 is in the form y = mx+b
m = -3 = -3/1 is the slope
slope = rise/run = -3/1
the "rise" being negative is really a fall or decrease. As we rise higher, the temperature goes down which is expected (It's colder higher up in the atmosphere)