plis na teraz z matematyki

a) (9dm+19dm)•12dm/2=28dm•12dm/2=
=336dm²/2=168dm²
b) 2dm=20cm
(16cm+23cm)•20cm/2=39cm•20cm/2=
=780cm²/2=390cm²
c) 0,5m=5dm ; 90cm=9dm
(6dm+9dm)•5dm/2=15dm•5dm/2=
=75dm²/2=37,5dm²