Let us prove that triangles ABC and DBE are similar.
By condition, DE is parallel to AC, then the angle CAB = EDB as the corresponding angles at the intersection of parallel straight lines AC and DE secant AB. Angle B is common for triangles.
Then triangles ABC and DBE are similar in two angles.
The coefficient of similarity of triangles is: K = DE / AC = 2/6 = 1/3.
Then DB / AB = 1/3.
AB = 3 * DB = 3 * 3 = 9 cm.
Answer: The length of the AB side is 9 cm.
One of the components of a person's success in our time is receiving modern high-quality education, mastering the knowledge, skills and abilities necessary for life in society. A person today needs to study almost all his life, mastering everything new and new, acquiring the necessary professional qualities.