If r=radius, volume of sphere=4πr³/3; volume of cone=πr²h/3, where h is the height of the cone. If the melted sphere is to fit into the cone,
4πr³/3≤πr²h/3, 4r≤h. So h≥4r, the height of the cone must be at least 4 times the radius of the sphere/cone. If r=5cm, h must be at least 20cm. So if the height is 10cm, it will not contain all the melted yoghurt.
a) No
b) 20cm