$a\text{)}5\cdot \left(9\cdot {10}^7\right)=45\cdot {10}^7=4,5\cdot 10\cdot {10}^7=4,5\cdot {10}^8$

$b\text{)}4\cdot {10}^3\cdot 7=28\cdot {10}^3=2,8\cdot 10\cdot {10}^3=2,8\cdot {10}^4$  

$c\text{)}8\cdot \left(3\cdot {10}^{-7}\right)=24\cdot {10}^{-7}=2,4\cdot 10\cdot {10}^{-7}=2,4\cdot {10}^{-6}$  

$d\text{)}\left(8\cdot {10}^6\right)\cdot \left(4\cdot {10}^9\right)=32\cdot {10}^6\cdot {10}^9=3,2\cdot 10\cdot {10}^6\cdot {10}^9=3,2\cdot {10}^{16}$  

$e\text{)}\left(7\cdot {10}^{-3}\right)\cdot \left(2\cdot {10}^7\right)=14\cdot {10}^{-3}\cdot {10}^7=1,4\cdot 10\cdot {10}^{-3}\cdot {10}^7=1,4\cdot {10}^5$   

$f\text{)}\left(16\cdot {10}^2\right):\left(8\cdot {10}^{-5}\right)=\frac{16\cdot {10}^2}{8\cdot {10}^{-5}}=\frac{16}{8}\cdot \frac{{10}^2}{{10}^{-5}}=2\cdot {10}^{2-\left(-5\right)}=2\cdot {10}^7$  

$g\text{)}5,4\cdot {10}^8+3\cdot {10}^{11}=5,4\cdot {10}^8+3000\cdot {10}^8=3005,4\cdot {10}^8=3,0054\cdot {10}^{11}$  

$h\text{)}1,8\cdot {10}^{12}-20\cdot {10}^9=1800\cdot {10}^9-20\cdot {10}^9=1780\cdot {10}^9=1,78\cdot {10}^{12}$  


$\text{* Korzystamy z łącznosˊci i przemiennosˊci mnoz˙enia.}$