$a)a=1\text{m}=10\text{dm}$

$P=\frac{1}{2}\cdot \left(10\text{dm}+8\text{dm}\right)\cdot 4\text{dm}=\frac{1}{{\sout{2}}^1}\cdot 18\text{dm}\cdot {\sout{4}}^2\text{dm}=36{\text{dm}}^2$

$b)b=13\text{cm}=1,3\text{dm}$

$P=\frac{1}{{\sout{2}}^1}\cdot \left(1\text{dm}+1,3\text{dm}\right)\cdot {\sout{2}}^1\text{dm}=2,3{\text{dm}}^2$

$c)b=2\text{dm}=20\text{cm}$

$P=\frac{1}{2}\cdot \left(7\text{cm}+20\text{cm}\right)\cdot 4\text{cm}=\frac{1}{{\sout{2}}^1}\cdot 27\text{cm}\cdot {\sout{4}}^2\text{cm}=54{\text{cm}}^2$

$d)b=53\text{cm}=5,3\text{dm}$

$h=400\text{m}=4000\text{dm}$

$P=\frac{1}{2}\cdot \left(2,5\text{dm}+5,3\text{dm}\right)\cdot 4000\text{dm}=\frac{1}{{\sout{2}}_1}\cdot 7,8\text{dm}\cdot {\sout{4000}}^{2000}\text{dm}=7,8\cdot 2000{\text{dm}}^2=15600{\text{dm}}^2$