The formula for the area (A) of a circle is A = πr² but this can also be stated as πd²/4 where r and d are the radius and diameter respectively.

A = πd²/4 = π x 12²/4 = π x 144/4 = π x 36 = 113.097 square inches.

A = πd²/4 = π x 12²/4 = π x 144/4 = π x 36 = 113.097 square inches.