-1" OR 5*5=26 --

That looks like a classic SQL injection payload, not a math problem.

High-level idea:

• The -1" attempts to break out of a string literal in a SQL query.
• The OR 5*5=26 adds a boolean expression to the query (in insecure code this could alter the WHERE clause).
• The -- starts a comment, so the rest of the original statement is ignored.

In insecure code that concatenates user input into SQL, such payloads can change the logic of the query (potentially bypassing authentication or exposing data). In well-secured code, such input should not alter the query at all.

Defensive measures you should know for exams:

• Use parameterized queries (prepared statements) with bound parameters, not string concatenation.
• Validate and sanitize input (whitelist allowed values, enforce types).
• Prefer ORM or DB APIs that automatically parameterize queries.
• Disable or restrict multi-statement execution and limit database privileges (least privilege).
• Handle errors safely (do not leak database error details to users).

If you want, I can give you a concise exam-ready paragraph describing this payload and the defenses. Would you like that?