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 \( \alpha u + \beta v = 18, \gamma u + \delta v = 20 \), then \( u + v \) equals:
