(a) Opportunity cost is defined as the highest-valued option forgone. The cost of buying the computer is the option of rnjoying the one-week tour in Japan.
(b) The cost of making the first choice is forgoing the tour to Japan. The cost of making the third choice is forgoing the computer. The two costs are not same.
(c) (i) The cost would be lower, since the value from choosing the tour to Japan would would be lower.
(c) (ii) The cost would remain unchanged, since the highest-valued option forgone is not affected.