Calculate the area of a sector with radius 21 cm and angle 90 degrees, using pi = 22/7.

The radius of the sector is $r = 21 \text{ cm}$.
The angle of the sector is $\theta = 90^\circ$.
We are given to use $\pi = \frac{22}{7}$.

The area of a sector is given by the formula:

First, simplify the fraction $\frac{90^\circ}{360^\circ}$:

Next, calculate $(21 \text{ cm})^2$:

Now, substitute these back into the area formula:

The area of the sector is $\text{346.5 cm}^2$.