The formula for the area of a circle is \(A = \pi r^2\), where \(r\) is the radius of the circle and \(\pi\) is approximately equal to \(\frac{22}{7}\).

Since the diameter of a circle is twice its radius, we can find the radius of this semi-circle by dividing its diameter by 2: \(r = \frac{d}{2} = \frac{42}{2} = 21\).

The area of a semi-circle is half the area of a full circle with the same radius, so we can use this formula to find the area of this semi-circle:

\(A = \frac{\pi r^2}{2}\)

\(A = \frac{\left(\frac{22}{7}\right) \times 21^2}{2} = 693\)