a)

1 dm² = 100 cm²

$\frac{1}{4}{\text{dm}}^2=0,25{\text{dm}}^2=25{\text{cm}}^2$  

  

$25{\text{cm}}^2=\frac{1}{4}{\text{dm}}^2$   

 

b)

1 m² = 10 000 cm² = 1 000 000 mm²

$0,04{\text{m}}^2=0,04\cdot 1000000{\text{mm}}^2=40000{\text{mm}}^2$  

$4000{\text{mm}}^2\ne 40000{\text{mm}}^2$    

 

c)

$1\text{a}=100{\text{m}}^2$    

 

d)

1 ha = 10 000 m²

$30000{\text{m}}^2=3\text{ha}$