Review the original item:
Tracy always knows the right answer in English class but is too shy to
volunteer whenever Professor Simmons asks a
question, Tracy's hand feels as if it weighs 1,000 pounds.
You chose the correct way to fix the error:
Tracy always knows the right answer in English class but is too shy to
volunteer;
whenever Professor Simmons asks a question, Tracy's hand feels
as if it weighs 1,000 pounds.
Tracy always knows the right answer in English class but is too shy to volunteer is a complete sentence. Whenever Professor Simmons asks a question, Tracy's hand feels ... begins the second complete sentence.
You are always correct when you use a semicolon to join two complete sentences that are closely related in meaning.