It's an over-simplified way of doing it, but the Astros are 10 games back with 38 to play, including three coming up with St. Louis. St. Louis is 72-54, Chicago is 62-60, the Astros are 61-63, and Milwaukee is 61-64. Let's pretend that every other team stays within their exact winning percentage for the rest of the season. That means...
St. Louis: 93-69
To catch the Cardinals, who would theoretically go 21-15, the Astros would need to go 32-6. Did I get that math right? Do I really care?