This online exercise has three levels. Try level 2. Follow the instructions on the screen. You can use the ‘check’ button at the bottom to see if you are correct.
If you are feeling very confident and looking for a tough challenge, you can try Level 3 instead but beware, it is tricky!
Tip for Level 3: read the ‘Symbols Used’ key in the bottom left corner of the timetable before you start - there is essential information there.