A coin with the probability of heads being 0.7 and a fair six-sided die are used for a random experiment. The coin is first tossed. If the outcome is heads, the die is thrown twice. If the outcome is tails, the die is thrown only once. Find the probability of:
(a) Throwing a sum less than 8.
(b) Throwing a sum of which is an odd number greater than or equal to 7.
(c) Throwing a sum of 8, 10 or 12.