Martingular Variance

Suppose that $\{Z_n\}_{n \geq 0}$ is a martingale, where $Z_0 = 0$. For $i \geq 1$, define $X_i = Z_i - Z_{i-1}$. Compute $\var{Z_n}$ when $n = 10$ and $\var{X_n} = n$.