To solve this problem, we can use the concept of constructive and destructive interference of sound waves.

Given:
Frequency of the oscillator, f = 425 Hz
Distance between the two speakers, d = 2.4 m
Velocity of sound in air, v = 340 m/s

Step 1: Finding the wavelength of sound
The wavelength of sound can be calculated using the formula:
wavelength = velocity / frequency
wavelength = 340 / 425 = 0.8 m

Step 2: Finding the path difference
As the person moves away from the speakers, the path difference between the sound waves reaching the person's ears from the two speakers will change. At certain positions, the path difference will result in destructive interference, and the person will hear no sound.

Let's assume the person is at a distance x from the pole.

The path difference between the sound waves from the two speakers reaching the person's ears can be calculated using the formula:
path difference = d * sin(theta)
where d is the distance between the speakers and theta is the angle between the line connecting the person's ears and the line connecting the two speakers.

In this case, theta is the angle between the horizontal line (as the person is running horizontally away from the speakers) and the line connecting the two speakers.

Step 3: Finding the maximum distance
To find the maximum distance at which the person hears no sound, we need to find the condition for destructive interference. This occurs when the path difference is equal to an integer multiple of the wavelength.

Thus, we can write the equation:
d * sin(theta) = n * wavelength
where n is an integer.

For destructive interference, the path difference should be equal to an odd multiple of half the wavelength.

So, we have:
d * sin(theta) = (2n + 1) * (wavelength / 2)

Rearranging the equation, we get:
sin(theta) = (2n + 1) * (wavelength / (2d))

To find the maximum distance, we need to find the maximum value of sin(theta), which occurs when sin(theta) is equal to 1.

So, we have:
1 = (2n + 1) * (wavelength / (2d))

Simplifying the equation, we get:
2d = (2n + 1) * wavelength

Substituting the values we have:
2 * 2.4 = (2n + 1) * 0.8

Solving the equation, we find:
4.8 = 0.8(2n + 1)

Simplifying further, we get:
2n + 1 = 6

Solving for n, we find:
n = 2

Substituting this value back into the equation, we get:
2d = (2 * 2 + 1) * 0.8
2d = 5 * 0.8
2d = 4
d = 2

Therefore, the maximum distance at which the person hears no sound is 2 meters from the pole.

However, the given answer is 7 meters, which seems to be incorrect based on the calculations. Please double-check the given answer or provide additional information if available.