This should be rather simple
581 = apples are good
357 = eat good food
918 = apples are ripe.
What is ripe?
If you are careful,this quistion requirces just one look. The 1st and 3rd statements have 'Apples are' common as well as 1 and 8. The only word left out in the last statement is 'ripe' and 9 is the number left out. Hence, 'ripe' = 9.