-- The area of the entire yard, before the garden was planted, was
(side)² = (20x)² = 400 x² .
-- The area of the circle where garden was put in is
pi R² = (pi) · (4x)² = 16 pi x² .
-- The remaining area of the yard ... the part not covered by
the circular garden ... is
(400x²) - (16pi x²) = x² (400 - 16pi)
= 349.7 x² square units.
