Dimension of the quotient space $\frac{C_{0}}{M}.$

Solution 1:

Consider the map

$$C_0 \to \mathbb R, (x_n) \mapsto x_1+x_2 + \dotsb + x_{10}.$$

It is surjective (you can always choose the first $10$ elements of the sequence as you desire, without changing the limit) and the kernel is $M$ by definition. Hence $C_0/M \cong \mathbb R$.