Agricultural Drainage and Salinity

An irrigation water sample has concentrations of soluble cations: $[\text{Na}^+] = 12.0\text{ meq/L}$, $[\text{Ca}^{2+}] = 5.0\text{ meq/L}$, and $[\text{Mg}^{2+}] = 3.0\text{ meq/L}$. The Sodium Adsorption Ratio ($SAR = \frac{[\text{Na}^+]}{\sqrt{([\text{Ca}^{2+}] + [\text{Mg}^{2+}])/2}}$) is: