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 $\alpha u + \beta v = 18$ and $\gamma u + \delta v = 20$, then $u + v$ equals:
Let for $x\in\mathbb{R}$, $S_0(x)=x$, $S_k(x)=C_kx+k\int_0^x S_{k-1}(t)\,dt$ where $C_0=1$, $C_k=1-\int_0^1 S_{k-1}(x)\,dx$, $k=1,2,3,\ldots$. Then $S_2(3)+6C_3$ is equal to _______.