Final answer:
By substituting the atmospheric temperature (-61.2 °F) and ground temperature (20 °F) into the formula and solving for altitude, we find that the closest altitude is approximately 23,200 feet, corresponding to option (c) 23,429 feet.
Step-by-step explanation:
To find the altitude where the atmospheric temperature is -61.2 °F when the ground temperature is 20 °F, we use the given formula: t = -0.0035a + g. Here, t is the atmospheric temperature, a is the altitude in feet, and g is the ground temperature.
- Insert the known values into the equation: -61.2 = -0.0035a + 20.
- Subtract 20 from both sides to isolate the terms with a: -61.2 - 20 = -0.0035a, which simplifies to -81.2 = -0.0035a.
- Divide both sides by -0.0035 to solve for a: a = -81.2 / -0.0035.
- Calculating the above expression provides us the altitude a: a ≈ 23,200 feet.
Therefore, the correct option is (c) 23,429 feet, since 23,200 feet is closest to this choice when rounding to the nearest options provided.