Final answer:
The equation appears to be a quadratic involving the variable m; however, there seems to be a typo or confusion due to the presence of an additional variable n. Without further information or correction, we can't solve the equation definitively.
Step-by-step explanation:
The equation provided by the student 12m + 5 = m² + 9m + 2mn represents a quadratic equation where the variable m needs to be solved. To do so, we should first aim to get all terms containing m on one side of the equation. However, this equation also has the term 2mn, indicating that we are dealing with more than one variable.
Assuming there's a typo and n should not be there, we would proceed by subtracting 12m and 5 from both sides to get the m terms alone. If the n is correct, we need information about the value of n or another equation relating m and n to solve this system.