Answer:
t=4.86s
Step-by-step explanation:
To find the wavelength you use the following formula:
![v=\lambda f](https://img.qammunity.org/2021/formulas/physics/middle-school/dslwgr2ddx8wc6dkcnsdffid08rk880a6s.png)
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:
![\lambda=(v)/(f)=(343m/s)/(400Hz)=0.85m](https://img.qammunity.org/2021/formulas/physics/middle-school/rjxya8wjiplw2zamefzc4s0pu7np0v18id.png)
Now, to calculate the time that sound takes to reach the last row you use:
![t=(d)/(v)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/ka63067yy0mzlngnvsr9icm0di80s75s7g.png)
t: time
d: distance to the last row = 1947m
![t=(1947m)/(400Hz)=4.86s](https://img.qammunity.org/2021/formulas/physics/middle-school/serlvy5tcd2ed4q11byy4i0kejmagssh2m.png)
hence, the time is 4.86s