Question on Pareto Optimality

Suppose there are 4 alternatives, x, y, z & w. Further suppose that there are 7 individuals, 1, 2, 3,4,5,6 & 7. The individuals' rankings (orderings) of the four alternatives, Ri, i = 1,..., 7 are given by:

R1: xIyPzPw
R2: yPzPwPx
R3: zPwPxIy
R4: xIyPzPw
R5: yPzPwPx
R6: zPwPxIy
R7: xIyPzPw

Determine which of the alternatives are Pareto optimal. Explain your answer.

Notation: xPy implies the individual prefers x to y and xIy implies the individual is indifferent to x & y.