Cut out the largest circle from the square iron sheet with a side length of four decimeters. What is the area of this circle?

Cut out the largest circle from the square iron sheet with a side length of four decimeters. What is the area of this circle?

Square area S1 = 4 * 4 = 16 (square decimeter)
Area of circle S2 = 3.14 * (4 / 2) ^ 2 = 3.14 * 4 = 12.56 (square decimeter)
So S2: S1 = 12.56:16 = 157 / 200