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
We already know the formula:
Voltage = Current * Resistance
In the given question, there are numerous information's that are already given.
Current = 6.2 A
Resistance = 18 ohms
Then
Voltage = 6.2 * 18 Volts
= 111.6 Volt
So, the voltage in the circuit will be 111.6 volts. I hope it helps you.
Explanation is in the file
tinyurl.com/wpazsebu
I think this is the answer:
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