EN connects certain adverbs to expressions of quantity: "We have
nearly 100 students", "I have about 50 dollars". Number words
therefore carry an optional EN-.

                        +----EN----+
                        |          |
        It will cost almost 400 million dollars
        They died    almost 400 million years ago

Note that the EN always connects to the head word of the
number expression: i.e., the word that connects it to the
rest of the sentence.