Suppose you see the following price quotation for stock options:

                       Calls                           Puts
              -----------------------         -----------------------
exercise      Mar       Jun       Sep         Mar       Jun       Sep
price
XYZ            4         5         6           1        2 1/2      3
XYZ            3        4 1/2      5         1 1/4      2 1/2    3 1/2
XYZ          2 1/2       3         4         1 1/2      3          4
ABC            1        2 1/2    3 1/4         4        5 1/2    6 1/4
ABC            4         5         6           1        2 1/2      3
III            4         5         6        8 1/2       9 1/4     10
III            3         4       5 1/2        10        12       14 1/2

a) -3
b) -7/120
c) +6

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