When a fair die is tossed, each of the six sides (numbers 1 to 6) is equally likely to land face up. Two fair dice, one red and one green, are tossed. Explain whether the following pairs of events are mutually exclusive, independent, both, or neither:
a. A = red die is a 3; B = red die is a 6.
b. A = red die is a 3; B = green die is a 6.