The matrix $M$ is:

$M = \begin{bmatrix} 0 & 6 \\ 8 & -26 \end{bmatrix}$

Would you like a detailed explanation on how this was derived, or do you have any questions?

Here are some related questions:

1. What would change if the equation were $A + M = 2B + C$?
2. How do you solve matrix equations in general?
3. What happens if you replace $C$ with a zero matrix in this equation?
4. Can you explain how matrix multiplication affects the dimensionality of the result?
5. How would you solve a system of linear equations using matrices?

Tip: When solving matrix equations, always ensure that the matrices involved are conformable for operations like addition, subtraction, or multiplication.