help me solve these 3 ques. plzz:

Q. 4  A cylindrical tub of radius 12 cm contains water to a depth of 20 cm. A spha•ical iron ball is dropped into the tub and thus the level of the water is raised by 6.75 cm. What is the radius of the sphere? 
(1) 9 cm (2) 3  cm          (3) 12 cm     (4) 18 cm


Q. 5 The height ofa cone is 30 cm. A small cone is cut off at the top by a plane parallel to its base. If its volume be 1/27 ofthe volume of the give cone, at which height above the base is the section cut ? 
(1) 10  cm    (2) 20  cm       (3) 15  cm      (4) 30  cm   

Q.6 Water in a canal, 30 dm wide and 12 dm deep, is following with a velocity of 20 km per hour. How much area will it irrigate in 30 min, if 9 cm of standing water is desired ? 
(1) 2 x 10⁵ m²        (2) 4 x 10⁵ m²        (3) 3 x 10⁵ m²           (4) 7 x 10⁵ m²