Answer:
15 because 5×5×5 is the same thing as 5×3 which equals to 15
If the two waves combine to produce ANY wave that smaller
than either of the originals, that's destructive interference.
The time described above is known as the waves Period.
The time which it takes for a particle to complete one full cycle is known as the period. Period is normally measured in seconds. Frequency on the other hand is the number of cycles which are completed in a given period of time e.g a second. periodic time T is given by reciprocal of frequency (1/f).
The answer would be 981 newtons or 220.46 pounds.