Final answer:
Without further context or information about the problem involving the length of side 'a', it's not possible to answer the question accurately or choose the closest option. Additional details are needed to provide the correct length of side 'a' rounded to the nearest tenth of a centimeter.
Step-by-step explanation:
To answer the question, "What is the length of side a rounded to the nearest tenth of a centimeter?", we need additional information about the specific situation or problem the student is working on. Since the provided information does not relate to a length of side 'a', it's not possible to select an option from choices A) 12.8 cm, B) 8 cm, C) 20.8 cm, and D) 21.6 cm without the context of the problem. For example, if the student is working on the Pythagorean theorem in a right triangle, they would need the lengths of the other two sides to compute the length of side 'a' using the formula a^2 = b^2 + c^2.