First, let's simplify each fraction individually:

(7x - x^2)/(x + 4) = -x(x - 7)/(x + 4)

(x^2 - x - 20)/(7 - x) = (x - 5)(x + 4)/(7 - x)

Now, we can multiply the two simplified fractions together:

(-x(x - 7)/(x + 4)) * ((x - 5)(x + 4)/(7 - x))

= [-x(x - 7)(x - 5)(x + 4)] / [(x + 4)(7 - x)]

Now, we can simplify further by canceling out common factors:

= [-x(x - 7)(x - 5)] / (7 - x)

So, the final simplified expression is:

(-x^3 + 12x^2 - 35x) / (7 - x)