Violet Gem Bracelet : MM18
It seems you pressed the correct button.
Two circles add up to 18, so one circle is 9.
If you add one circle to the sum of the triangle and the square,
you get the answer to the question.
So, adding 9 to 4 gives you 13 as the answer.
You press the 13 button beneath the frame.
Soon, a part of the wall beneath the buttons opens,
and the Violet Bracelet treasure is revealed.
You take the treasure from the small space
inside the opened section of the wall and secure it.
After obtaining the treasure, you leave the area.
You make your way out.
You successfully secure the treasure.
Congratulations!