a) 20% z 80 to:
$20\%\cdot 80=\frac{20}{10\sout{0}}\cdot 8\sout{0}=\frac{2\sout{0}}{1\sout{0}}\cdot 8=16$  

Zatem: 
20% z 80 zł  > 15 zł  
$\underline{\underline{}}$ $\underline{\underline{}}$  

b) 120% z 200 to:
$120\%\cdot 200=\frac{120}{1\sout{00}}\cdot 2\sout{00}=120\cdot 2=240$   

Zatem:
120% z 200 zł  < 250 zł
$\underline{\underline{}}$  

c) 55% z 90 to:
$55\%\cdot 90=\frac{55}{10\sout{0}}\cdot 9\sout{0}=\frac{55\cdot 9}{10}=49,5$  

Zatem:
55% z 90 zł  < 50 zł
$\underline{\underline{}}$  

d) 150% z 600 to:
$150\%\cdot 600=\frac{150}{1\sout{00}}\cdot 6\sout{00}=150\cdot 6=900$  

Zatem:
150% z 600 zł  < 1000 zł