Rút gọn:

1. $A = {{x + 8} \over {x - 2}}.{{3x - 7} \over {x + 10}} + {{x + 8} \over {x - 2}}.{{5 - 2x} \over {x + 10}}$

2. $B = \left( {{x \over {x + y}} + {x \over {x - y}}} \right).\left( {{x^2} - {y^2}} \right)$

3. $C = {{{x^2} + 3x} \over {{x^2} + 3x + 9}}.{{{x^3} - 27} \over {4x + 12}}.$