Answer:
C. 2.8 miles per minute
Step-by-step explanation:
The mnemonic SOH CAH TOA reminds you that ...
... Tan = Opposite/Adjacent
In the relevant triangle, the side opposite the angle at the observer is the altitude of the airplane, 2 miles. The side adjacent is the horizontal distance to the airplane. At the first observation, that distance (d1) is ...
... tan(40°) = (2 mi)/d1
At the second observation, the horizontal distance to the airplane (d2) is ...
... tan(50°) = (2 mi)/d2
Solving for d1 and d2 and finding the difference (∆d), we have ...
... d1 = (2 mi)/tan(40°)
... d2 = (2 mi)/tan(50°)
... ∆d = d1 -d2 = (2 mi)(1/tan(40°) -1/tan(50°) ≈ 2·(1.1918 -0.8391) mi
... ∆d ≈ 2°0.3526 mi ≈ 0.7053 mi
This distance was flown by the plane in 15 seconds, so it will travel 4 times this distance in 60 seconds (1 minute).
... ∆d/∆t = (0.7053 mi)/(1/4 min) = 4·0.7053 mi/min ≈ 2.8 mi/min
