((x^2-4x-21)/(7x)) / ((x+3)/(x+7)) * ((x^2-7x)/(x^2-14x+49))
((x + 3)((x - 7)/7x) / ((x + 3)(x + 7)) * (((x(x -7))/(x - 7)^2)) first step take out the (x + 3)
((x-7)/7x) / (x + 7) * (((x(x - 7)/(x - 7)^2)) step two remove the (x - 7) (Second factor)
(x-7)/7x / (x + 7)x/(x - 7)) step three flip the second factor and multiply
(x-7)/7x * (x-7)/(x+7)x
(x - 7)^2/7x^2(x + 7)