The implementation of the PBL activity involves several phases: introduction, investigation, solution, presentation, and reflection. In the introduction phase, you present the problem to the students and explain the learning outcomes, expectations, and assessment criteria. You also help the students form groups and assign roles and responsibilities. In the investigation phase, the students research the problem, gather and evaluate information, and generate ideas and hypotheses. You facilitate their inquiry and monitor their progress, but avoid giving direct answers or solutions. In the solution phase, the students synthesize their findings and develop a solution or a product that addresses the problem. You guide their decision-making and problem-solving, and encourage them to be creative and innovative. In the presentation phase, the students share their solution or product with an audience, such as their peers, teachers, or experts. You provide them with opportunities to communicate their process and outcomes, and to receive and give feedback. In the reflection phase, the students evaluate their own and their group's performance, as well as their learning and growth. You help them identify their strengths and weaknesses, and set goals for improvement.