Examine the clock in the bookcase. The four symbols correspond to the numbers 3, 6, 9 and 12. The symbols for 3 and 6 are identical to two of the symbols on the wooden blocks. Although 9 and 12 are not needed for the combination, studying all four symbols will help in working out the association between numbers and symbols.
Count the number of angles (or corners) in the four symbols. The 3 has three, the 6 has six, the 9 has nine and the 12 has twelve!
By counting the angles on the wooden block symbols you can work out their corresponding numbers.
Transfer the blocks from the bottom to the top row as shown above, then lower the handle to open the safe.