Pawan has a solid sphere of radius 21 cm. He melted it to form a cube. 20% material is wasted in this process. He melted the cube to form hemisphere. In this process 20% material is wasted. He again melted hemisphere to form two spheres of equal radius. 20% material was again wasted in this process. Then find the radius (in cm) of each new sphere?

Original sphere volume = (4/3)π × 21³ = 4116π cm³. After 20% waste in forming cube: remaining = 0.8 × 4116π. Cube volume = (0.8 × 4116π) = side³. After 20% waste to hemisphere: remaining = 0.64 × 4116π. Hemisphere volume = (0.64 × 4116π) = (2/3)πr³. After 20% waste to 2 new spheres: total remaining = 0.512 × 4116π = 2 × (4/3)πR³. Solving: R³ = (0.512 × 4116π × 3)/(8π) = 793.824. R = ∛793.824 = 8.4∛4 cm. Options A, B, and C have incorrect coefficients or cube roots.