METEOROLOGY In stable air, as the altitude of a weather balloon increases, the temperature drops at a rate of about $5^{\circ} \mathrm{F}$ for each 1,000 -foot rise in altitude.
(A) If the temperature at sea level is $70^{\circ} \mathrm{F}$, write a linear equation that expresses the temperature $T$ in terms of altitude $A$ (in thousands of feet above sea level).
(B) What would the temperature be at an altitude of 10,000 feet?
(C) What is the slope of the graph of the equation found in part A? What does the slope describe physically?