$a)$

$\left|12-5\right|=\left|7\right|=7$

$b)$

$\left|0,05-0,25\right|=\left|-0,2\right|=0,2$ $\left|0,05-0,25\right|=\left|-0,2\right|=0,2$

$c)$  

$\left|1,5-1\frac{3}{4}\right|=\left|-0,25\right|=0,25$   

$d)$

$\left|-4\right|\cdot \left|-3\right|-\left|-5\right|-\left|20\right|=4\cdot 3-5-20=12-25=-13$

$e)$

$-\left|100\right|:\left|-50\right|-\left|2\right|=-100:50-2=-2-2=-4$

$f)$

$\left|-120\right|:\left|-2\right|-\left|-3\right|\cdot \left|6\right|-\left|-7\right|=120:2-3\cdot 6-7=60-18-7=35$  

$g)$    

$\frac{\left|115\right|-\left|-11\right|}{\left|4-5\right|}\cdot \frac{3}{26}=\frac{115-11}{\left|-1\right|}\cdot \frac{3}{26}={\sout{104}}^4\cdot \frac{3}{{\sout{26}}^1}=12$   

$h)$

$\frac{\left|-\right|-5\left|+14\right|}{\left|-3\right|\cdot \left|2\right|-\left|-2\right|}\cdot \frac{\left|-3\right|\cdot 4}{\left|-\right|-6\mid \mid }=\frac{\left|-5+14\right|}{3\cdot 2-2}\cdot \frac{3\cdot 4}{\left|-6\right|}=\frac{\left|9\right|}{6-2}\cdot \frac{12}{6}=\frac{9}{4}\cdot 2=4\frac{1}{2}$