Several Spanish teachers (e.g., "Spanish with Vicente," "Tu escuela de español") have created playlists solving Aula Internacional exercises page by page. Search for "Corrección ejercicios Aula Internacional 4."

When searching for "aula internacional plus 4 libro del profesor y respuestas pdf", ensure you are getting the Plus version.

Using an answer key from the old version for the Plus book will lead to frustration—the page numbers and exercises do not match.

Some publishers sell a slim, cheap booklet containing only the exercise solutions (without the didactic guides). Check if Difusión offers a "Solucionario" separate from the full teacher’s guide.