Find the least common denominator (LCD) of the rational expressions:

(a) $\displaystyle \frac{6 x}{x^2 + 8x+16}, \quad \frac{3 x}{x^2+2 x - 8}$:  

(b) $\displaystyle \frac{x}{x^2 - 64}, \quad \frac{7}{40 - 5 x}, \quad \frac{4}{x}$: