I very much doubt that they'll make $4 billion next year. They did it this year because Black Panther was an unexpected $1.3 billion surprise (And I suspect that Black Panther 2 won't repeat that phenomenon, and will come in with a smaller take). One which won't be repeated next year. Not with Spider-Man or Captain Marvel.
I'm absolutely positive that that Avengers 4 will not only make $2 billion, but will outdo Infinity War, but they still need to make about $1.9 billion to hit $4 billion. And it's highly unlikely that both Spider-Man and Captain Marvel will hit that mark. I think they'll ballpark around $800-$900 million, which still leaves them $100-300 million short.