A coin is tossed twice. Let Z denote the number of heads on the first toss and W the total number of heads on the 2 tosses. If the coin is unbalanced and a head has a 40% chance of occurring, find
a) The joint probability distribution of W and Z;
b) The marginal distribution of W;
c) The marginal distribution of Z;
d) The probability that at least 1 head occurs.