You need a test case where there is no row in toys for the people_id. I didn't handle for this edge case, and my code still passed. Of course, maybe this shouldn't be at such a low level if it uses NVL. Maybe clarify the assumption that there will always be a record in toys.

Are we just suppoed to assume the foreign key here? It seems like it should be specified.

The phrasing of the description is very vague. Suggested:
In a small town, the starting population is p0 = 1000. Each year, the population naturally increases by 2 percent and also increases by 50 due to migration. How many years does the town need to see its population greater or equal to p = 1200 inhabitants?

This needs a test case where p0 is already >= p.