$($a$)$ Apply SHA$-256$ to hash a $3000-$bit message. How many compression function operations are needed to hash the message?

$($b$)$ After downloading a file from a server, the user computes the checksum of the file using SHA$-256,$ then compare the computed checksum with the SHA$-256$ checksum of that file stored at the server. The user would discard the downloaded file if there is any mismatch between these two checksums.

A SHA$-256$ checksum consists of $32$ hexadecimal characters. Suppose that the user does not compare all those $32$ hexadecimal characters, but compares only the first $5$ hexadecimal characters and the last $4$ hexadecimal characters of the checksums. If there is an error in the downloaded file, what is the probability that the wrong file would be accepted as correct file?