This Headline Story involves several steps. A first approach might be to make it concrete by having students pick a total cost and cost for the apples. Then help students to generalize their procedure.
The cost of the oranges and the grapes together is the difference between the total cost and the cost of the apples. If the apples cost $3, and the total cost was $15, then the cost of the oranges and the grapes together would be $12. Since the oranges cost the same amount as the grapes, they each must cost $6, or half of $12.