Answer:
The correct option is
Step-by-step explanation:
The parameters given are;
The length of the string = 10 inches
The speed or rate of travel of the wave = c inches per millisecond
The position on the string from the left-most end = x
The time duration of motion of the vibration to reach x= 0.3 milliseconds
The distance covered = Speed × Time = c×0.3
Given that the string is plucked at the middle, with the vibration travelling in both directions, the point after 0.3 millisecond is x where we have;
The location on the string where it is plucked = center of the string = 10/2 = 5 inches
Distance from point of the string being plucked (the center of the string) to the left-most end = 5 inches
Therefore, on the left side of the center of the string we have;
The distance from the location of the vibration x (measured from the left most end) to the center of the string = 5 - x = -(x -5)
On the right side of the center, the distance from x is -(5 - x) = x - 5
Therefore, the the equation that can be used to find the location of the vibration after 0.3 milliseconds is 
or 
which gives the correct option as A
