The Ljung Box statistic, also known as the modified Box Pierce statistic, is a function of the accumulated autocorrelations, $\rho_j$, up to time lag $m$. It’s calculated as:

$$Q(m) = n(n + 2) \sum \left[ \frac{\rho_j^2}{n - j} \right]$$

In this case, time lag = 3

Thus,

$$Q(3) = 333(335)\left[ \frac{0.12^2}{332} + \frac{(-0.17)^2}{331} + \frac{(-0.09)^2}{330} \right] = 17.32$$