i) we have,

Radius of cone = 6 cm

Height of cone = 7 cm

So, volume of cone = πr²h = 1/3 × 22/7 ×36×7 = 264 cm³

ii) we have,

radius = 3.5 cm

height = 12 cm

volume of cone = 1/3×22/7×3.5×3.5×12 = 154 cm³

iii) we have,

height = 21 cm

slant height = 28 cm

radius r = √(28²-21²) = √49×7 = 7√7 cm

volume of cone = 1/3×22/7×7√7×7√7×21 = 7546 cm³