The perimeter of a sector of a circle is given by the formula:

Perimeter = radius × angle in radians + 2 × radius

However, since the angle is given in degrees and the formula for the circumference of a circle (which is part of the perimeter of the sector) uses radians, we first need to convert the angle from degrees to radians. We know that 180° is equal to π radians, so:

120° = 120 × (\frac{\pi}{180}) = (\frac{2\pi}{3}) radians

Now we can substitute the values into the formula:

Perimeter = 10.5 × (\frac{2\pi}{3}) + 2 × 10.5

We are given that (\pi = \frac{22}{7}), so substituting this in gives:

Perimeter = 10.5 × (\frac{2 \times \frac{22}{7}}{3}) + 2 × 10.5 = 22 + 21 = 43 cm