Просто не понимаю....

Решите задачу:

$1)\frac{14b^{2} }{5}-\frac{9b^{2} }{5}=\frac{14b^{2}-9b^{2}}{5}=\frac{5b^{2} }{5}=b^{2} \\\\2)\frac{12b}{7}-\frac{3b}{7}=\frac{12b-3b}{7}=\frac{9b}{7}\\\\ 3)\frac{1}{a+b}-\frac{1}{a-b}=\frac{a-b-a-b}{(a-b)(a+b)}=-\frac{2b}{a^{2}-b^{2}}\\\\4)\frac{2}{3a}+\frac{b}{c}=\frac{2c+3ab}{3ac}$

$5)\frac{2a-4}{4a} +\frac{3a+4}{4a}=\frac{2a-4+3a+4}{4a}=\frac{5a}{4a}=\frac{5}{4}=1,25\\\\6)\frac{3}{ab}-\frac{b}{2ac} =\frac{6c-b^{2} }{2abc}\\\\7)\frac{1}{a^{2}b^{2}}-\frac{1}{ab}=\frac{1-ab}{a^{2}b^{2}}\\\\8)\frac{5}{x-5}-\frac{x}{x-5}=\frac{5-x}{x-5}=-\frac{x-5}{x-5}=-1$