Let the number of oranges be X, then the number of rambutans=5X so the total amount of fruit=X+5X=6X.
When we increase the number of rambutans we get 5X+609. We still have X oranges but the ratio changes: X/(5X+609)=3/44.
Cross-multiplying: 44X=3(5X+609)=15X+1827, 29X=1827, X=63 oranges.
[So originally there would have been 378 fruit, consisting of 63 oranges and 315 rambutans. When 609 rambutans are added, we then have 924 rambutans, so the ratio changes to 63/924=3/44, and there would be 987 fruit.]