After coming back from school you start in your room. On the floor are some glass shards. Collect the shards and open your rucksack. Highlight the shards and press Y and then highlight the image of a mirrors and press Y. Nika should tell you this works and the achievement will be awarded.
Update: Mental Knight 5 is correct first you will need to collect the Tesla poster from the wall in the same room before this will allow you to combine items. Many thanks
