Assume you mean 4 fruits (all possible mixtures of apples and oranges) with the given constraints for arranging in a line. Four identical fruits disobey the constraints.
(1) 3 apples and an orange:
{ AAOA, AOAA, OAAA }
(2) 2 apples and 2 oranges:
{ AAOO, AOAO, AOOA, OAAO, OAOA, OOAA }
(3) 1 apple and 3 oranges:
{ AOOO, OAOO, OOAO, OOOA }
Total arrangements from the sets=13.