Four Quarter-Circles in a Square
Compose the leftover region
A 6×6 square has four quarter-circles bitten out of each corner. Tap the curved leftover region in the middle to shade it green, then compute its area.
Composite Figure
Tap the regions to shade, then enter the area. Outer side = 6, radius = 3.
0 / 1 shaded
Tap target regions
Tip: green = shaded, blue = unshaded. Tap a region again to unshade it.