Struggling is part of learning. Before glancing at the PDF, spend a solid 10 minutes trying to solve a problem. Use your textbook notes, ask a friend, or re-read the example.
Several platforms host educational documents, lesson plans, and solution keys specifically for the Mathayomsuksa 3 level: Math Solution Mathayomsuksa 3 Pdf
Before an O-NET or final exam, print a few challenging problems from the solution PDF. Erase the answers. Timed yourself solving them. Then check against the PDF. This mimics real exam conditions. Struggling is part of learning