Spherical bowl is quarter full when 6 litres of water is poured into it. It implies that 4*6=24 litres is the volume of the bowl.
And 24 litres = 24000 cc
Volume of a spherical bowl = 4/3 * pi * r^3
24000 = 4/3 * 22/7 * r^3
or r^3 = (24000*3*7) / (4*22)
or r = 17.892 cm. (approx)