This question asks you to imagine — so there is no single right answer. But a good imagined story must still make sense with the real story: the ball is in the basket of a moving scooter, and the rider does not know it is there.
What a good answer needs: say where the scooter goes, how the ball leaves the basket, who picks it up, and what happens to it in the end. Write it as a small story, in full sentences.
Sample answer: The scooter turned left at the corner and went down the main road. The ball sat quietly in the basket among a packet of onions and a bundle of coriander. The scooterist rode home, parked the scooter and carried the vegetables inside. He never once looked at the ball. In the evening his little daughter, Meera, came out to take her cycle. She saw the white ball in the basket and shouted, “Whose ball is this?” Her father was as surprised as she was. He said it must have flown in from somewhere on the way. Meera was learning hockey at school, and she had no ball of her own. So she kept it for two days and asked at her school about it. When nobody claimed it there, her father took her back along the same road. They saw a playground with a gate, and some children playing hockey inside. Meera walked in and held up the ball. Gopi and his friends began to laugh all over again — and this time Meera stayed and played with them.
What makes this a good imagined ending: It keeps every fact of the real story — the basket, the rider who does not notice, the road past the playground. It only adds what the story left out. An imagined answer should never break the facts you were given.