Answer: Your Red Delicious apples needs a pollinator (such as Golden Delicious) in order to set fruit. Your new Granny Smith apple was growing near other apple types at the nursery and was pollinated which is why it is developing apples at this time. Now that you have both Red Delicious and Granny Smith in your garden, they should pollinate one another and you should have fruit from both next year. 75 feet apart is just fine - the pollinating insects will find the flowers.
Best wishes with your trees!
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