Answer: Choice C
Step-by-step explanation:
Start with the set {1, 2, 3, 4, 5, 6}
Stick "H" in front of each item to get {H1, H2, H3, H4, H5, H6} which represents half of the sample space. Something like H2 means "coin flipped heads and the number cube rolled a 2".
The other half of the sample space involves replacing each H with T. Which explains how we get T1, T2, T3, T4, T5, T6
Overall, the sample space is:
{H1, H2, H3, H4, H5, H6, T1, T2, T3, T4, T5, T6}
It might help to organize things into a table like this:

Or it could be written like this:

Either table demonstrates how there are 6*2 = 12 items in the sample space.