a) 

Zamieniamy na milimetry kwadratowe:

$1{\text{cm}}^2=1\text{cm}\cdot 1\text{cm}=10\text{mm}\cdot 10\text{mm}=100\text{mm}{}^2$  

$2{\text{cm}}^2=2\cdot 1{\text{cm}}^2=2\cdot 100{\text{mm}}^2=200\text{mm}{}^2$  

$5{\text{cm}}^2=5\cdot 1{\text{cm}}^2=5\cdot 100{\text{mm}}^2=500\text{mm}{}^2$  

$10{\text{cm}}^2=10\cdot 1{\text{cm}}^2=10\cdot 100{\text{mm}}^2=1000\text{mm}{}^2$

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b)

Zamieniamy na centymetry kwadratowe:

$1{\text{m}}^2=1\text{m}\cdot 1\text{m}=100\text{cm}\cdot 100\text{cm}=10000\text{cm}{}^2$  

$2{\text{m}}^2=2\cdot 1{\text{m}}^2=2\cdot 10000{\text{cm}}^2=20000\text{cm}{}^2$  

$7{\text{m}}^2=7\cdot 1{\text{m}}^2=7\cdot 10000{\text{cm}}^2=70000\text{cm}{}^2$  

$20{\text{m}}^2=20\cdot 1{\text{m}}^2=20\cdot 10000{\text{cm}}^2=200000\text{cm}{}^2$  

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c) 

Zamieniamy na decymetry kwadratowe:

$1{\text{m}}^2=1\text{m}\cdot 1\text{m}=10\text{dm}\cdot 10\text{dm}=100\text{dm}{}^2$  

$5{\text{m}}^2=5\cdot 1{\text{m}}^2=5\cdot 100{\text{dm}}^2=500\text{dm}{}^2$  

$9{\text{m}}^2=9\cdot 1{\text{m}}^2=9\cdot 100{\text{dm}}^2=900\text{dm}{}^2$  

$30{\text{m}}^2=30\text{m}\cdot 1\text{m}=30\cdot 100{\text{dm}}^2=3000\text{dm}{}^2$