$a)$

$1,2{\text{dm}}^2=1,2\cdot 10\text{cm}\cdot 10\text{cm}=120{\text{cm}}^2$

$0,04{\text{m}}^2=0,04\cdot 100\text{cm}\cdot 100\text{cm}=400{\text{cm}}^2$

$452{\text{mm}}^2=452\cdot 0,1\text{cm}\cdot 0,1\text{cm}=4,52{\text{cm}}^2$

$3,4\text{a}=3,4\cdot 100{\text{m}}^2=340{\text{m}}^2=340\cdot 100\text{cm}\cdot 100\text{cm}=3400000{\text{cm}}^2$ $3,4\text{a}=3,4\cdot 100{\text{m}}^2=340{\text{m}}^2=340\cdot 100\text{cm}\cdot 100\text{cm}=3400000{\text{cm}}^2$

 

$b)$

$40,5{\text{dm}}^2=40,5\cdot 0,1\text{m}\cdot 0,1\text{m}=0,405{\text{m}}^2$

$312,8{\text{cm}}^2=312,8\cdot 0,01\text{m}\cdot 0,01\text{m}=0,03128{\text{m}}^2$

$0,047\text{ha}=0,047\cdot 10000{\text{m}}^2=470{\text{m}}^2$

$0,24\text{a}=0,24\cdot 100{\text{m}}^2=24{\text{m}}^2$

 

$c)$

$35{\text{m}}^2=35\cdot 0,01\text{a}=0,35\text{a}$

$43,2{\text{dm}}^2=43,2\cdot 0,1\text{m}\cdot 0,1\text{m}=0,432{\text{m}}^2=0,00432\text{a}$

$21500{\text{cm}}^2=21500\cdot 0,01\text{m}\cdot 0,01\text{m}=2,15{\text{m}}^2=0,0215\text{a}$

$0,904\text{ha}=0,904\cdot 10000{\text{m}}^2=9040{\text{m}}^2=90,4\text{a}$

 

$d)$

$580{\text{m}}^2=580\cdot 0,0001\text{ha}=0,058\text{ha}$

$0,47{\text{km}}^2=0,47\cdot 100\text{ha}=47\text{ha}$

$4350{\text{dm}}^2=4350\cdot 0,1\text{m}\cdot 0,1\text{m}=43,5{\text{m}}^2=43,5\cdot 0,0001\text{ha}=0,00435\text{ha}$

$309\frac{2}{5}\text{a}=309,4\text{a}=309,4\cdot 0,01\text{ha}=3,094\text{ha}$