Let $\alpha , \beta , \gamma$ and $\delta$ be the coefficients of $x ^ { 7 } , x ^ { 5 } , x ^ { 3 }$ and $x$ respectively in the expansion of $\left( x + \sqrt { x ^ { 3 } - 1 } \right) ^ { 5 } + \left( x - \sqrt { x ^ { 3 } - 1 } \right) ^ { 5 } , x > 1$. If u and v satisfy the equations $\begin{aligned} & \alpha u + \beta v = 18 \\ & \gamma u + \delta v = 20 \end{aligned}$ then $u + v$ equals :\\
(1) 5\\
(2) 3\\
(3) 4\\
(4) 8