Did you say monkey business? Trophy in Subject 13

Story related and cannot be missed.

In chapter four, you will find yourself outside of a temple. Scattered around the area are gold plaques with Mayan numbers you can reveal using a special crystal found in the area. You have to do some maths and add these numbers up based on the category they're in (eye, mouth, ear) then translate that number into Mayan base-20 and align a key to represent these numbers in order to unlock the three monkey statues.

For an easier ride, just use my walkthrough to get the quick and easy answer as this puzzle is (thankfully) not randomized.