$\text{a)}1\frac{7}{8}\cdot \frac{4}{7}=\frac{15}{{\sout{8}}^2}\cdot \frac{{\sout{4}}^1}{7}=\frac{15}{14}=1\frac{1}{14}$  

$\text{b)}3\frac{1}{5}\cdot \left(-7\frac{1}{2}\right)=\frac{{\sout{16}}^8}{{\sout{5}}^1}\cdot \left(-\frac{{\sout{15}}^3}{{\sout{2}}^1}\right)=-24$  

$\text{c)}-12:4\frac{1}{2}=-12:\frac{9}{2}=-{\sout{12}}^4\cdot \frac{2}{{\sout{9}}^3}=-\frac{8}{3}=-2\frac{2}{3}$  

$\text{d)}4,15:\frac{5}{6}=4\frac{15}{100}:\frac{5}{6}=4\frac{3}{20}:\frac{5}{6}=\frac{83}{{\sout{20}}^{10}}\cdot \frac{{\sout{6}}^3}{5}=\frac{249}{50}=\frac{498}{100}=4,98$  

$\text{e)}24,8\cdot 2\frac{1}{10}=24\frac{8}{10}\cdot \frac{21}{10}=24\frac{4}{5}\cdot \frac{21}{10}=\frac{124}{5}\cdot \frac{21}{10}=\frac{2604}{50}=\frac{5208}{100}=52,08$  

$\text{f)}-\left(-100,56\cdot 3,12\right)=100,56\cdot 3,12=100\frac{56}{100}\cdot 3\frac{12}{100}=\frac{10056}{100}\cdot \frac{312}{100}=\frac{3137472}{10000}=313,7472$  

$\text{g)}-\left(-9\right):\left(-3,75\right)=-9:3\frac{75}{100}=-9:3\frac{3}{4}=-9:\frac{15}{4}=-{\sout{9}}^3\cdot \frac{4}{{\sout{15}}^5}=-\frac{12}{5}=-2\frac{2}{5}$  

$\text{h)}-\frac{1}{1000000}:0,001=-\frac{1}{1000000}:\frac{1}{1000}=-\frac{1}{1000000}\cdot 1000=-\frac{1}{1000}=-0,001$