Benjamin Franklin was both a statesman and an inventor. what is the correct way to parallel this sentence?

The sentence is correct as is. The two descriptors of Benjamin Franklin are nouns preceded by the correct article. You couldn't make it better!!

To correctly parallel the sentence "Benjamin Franklin was both a statesman and an inventor," you want to maintain consistency in structure. Here's one way to parallel the sentence:

"Benjamin Franklin was not only a statesman but also an inventor."

In this parallel structure, "not only" and "but also" are used to connect the two elements in the sentence - "a statesman" and "an inventor."