All of the sentences contain correctly placed modifiers except John spent about three years working in the hospital.

John spent about three years working in the hospital.

I accidentally threw away the report I wrote in the trash.

I accidentally threw away the report I wrote in the trash.

The baby elephant weighed nearly 625 pounds.

The baby elephant weighed nearly 625 pounds.

Henry spent just three months in the program.

Henry spent just three months in the program.