"He has such delicious apples!"
Translation:У него такие вкусные яблоки!
I will try to explain. The 3rd person personal pronouns ( her eë, his eго, their их) in any case , add H at their beginning when they occur after a preposition including у . For example, У Него есть чемодан, He has( by him there is) a suitcase . You have to differentiate third person personal pronouns from possessive pronouns however like his brother. Possessive pronouns never change after a preposition. For example, у его брата есть чемодан. His brother has( by his brother there is) a suitcase. I hope this is helpful.
Here, the English phrasing is a little difficult. The most natural way would be to have the exercise demand 'His apples are so delicious'. Generally, you are to omit есть from any phrase where the 'having' is natural or inherently connected to the owner. For example, you probably have a nose (if not, I'm sorry, they're great), so I'll tell you 'У тебя нос', you have a nose. But the есть is not there, because surprise surprise, people have noses in general. If you were a collector of noses, a есть would be used.
Why яблоки and not яблока? Edit: turns out the plural is irregular. https://en.m.wiktionary.org/wiki/%D1%8F%D0%B1%D0%BB%D0%BE%D0%BA%D0%BE