Answer:
t = 20.96 seconds
Step-by-step explanation:
given,
lightning strikes at = 4.5 mi( 23,760 ft)
air temperature =74.0°F
74.0°F = 23.3 °C
speed of the sound at 23.3 °C
V = 331.5 + 0.6 × T
V = 331.5 + 0.6 × 23.3
= 345.48 m/s
distance given = 4.5 mile
1 mile = 1609.4
4.5 mile = 4.5 × 1609.4 = 7242.3 m
time taken =


t = 20.96 seconds
hence, time taken by the sound to reach by the observer is 20.96 sec.