Again consider the set-up of the previous problem, except discard the last assumption there, that 30% of the birds currently live on island A and 70% live on B. Let y denote the (unknown) fraction of birds that live on B right now. Which of the following equations might we use to determine y such that next year, the same fraction of birds lives on island B? (a) 0.6 y + 0.9 (1 y) = y (b) 0.6 (1 y) + 0.9 y = y (c) 0.6 y + 0.9 (1 y) = 1 y (d) 0.6 (1 y) + 0.9 y = 1 y