B. 18 though now I believe it’s 17
A white-blue star is indeed hotter than a red star. So True :)
Answer:
t=4.86s
Explanation:
To find the wavelength you use the following formula:

v: speed of sound = 343m/s
f: frequency = 400Hz
λ: wavelength of the sound
By doing λ the subject of the formula and replacing the values of f and v you obtain:

Now, to calculate the time that sound takes to reach the last row you use:

t: time
d: distance to the last row = 1947m

hence, the time is 4.86s