Final answer:
A 64-QAM scheme is being used.
Step-by-step explanation:
In QAM (Quadrature Amplitude Modulation), each symbol represents a combination of two amplitude levels and two phase levels.
For 6 data bits to be represented in a single QAM symbol, we can use a 64-QAM scheme. In 64-QAM, each symbol represents 6 bits (2^6 = 64).
Therefore, if 6 data bits are used to represent a single QAM symbol, a 64-QAM scheme is being used.