$3\cdot {10}^7=3\cdot 10000000=300000003\backslash cdot10^7\backslash \; =\backslash \; 3\backslash cdot10\backslash \; 000\backslash \; 000\backslash \; =\backslash \; 30\backslash \; 000\backslash \; 000$

$\mathrm{6,4}\cdot {10}^{-4}=\mathrm{6,4}\cdot \mathrm{0,0001}=\mathrm{0,00064}6\{,\}4\backslash cdot10^\{-4\}\backslash \; =\backslash \; 6\{,\}4\backslash \; \backslash cdot0\{,\}0001\backslash \; =\backslash \; 0\{,\}00064$

$\mathrm{1,6}\cdot {10}^{-6}=\mathrm{1,6}\cdot \mathrm{0,000001}=\mathrm{0,0000016}1\{,\}6\backslash cdot10^\{-6\}\backslash \; =\backslash \; 1\{,\}6\backslash \; \backslash cdot0\{,\}000001\backslash \; =\backslash \; 0\{,\}0000016$

$\mathrm{7,4}\cdot {10}^9=\mathrm{7,4}\cdot 1000000000=74000000007\{,\}4\backslash cdot10^9\backslash \; =\backslash \; 7\{,\}4\backslash cdot1\backslash \; 000\backslash \; 000\backslash \; 000\backslash \; =\backslash \; 7\backslash \; 400\backslash \; 000\backslash \; 000$