The part we don't know is the replacement for "7b1e5cca". It's a hexadecimal 32-bit number, so there are 4,294,967,296 possible combinations. I don't think brute force will be fast enough to find it. The one thing we know about that code (assuming it's exactly like the previous ones) is that it's equal to the first 8 characters of the SHA-1 hash for the ZIP file. Unfortunately, without the ZIP file, we don't know the SHA-1 hash. And of course, if we had the ZIP file, we wouldn't need to find it.