a) P=a•h= 6 cm•3 cm=18 cm2
b) P= 1/2• d1•d2= 1/2•4 cm • 10 cm = 2 cm • 10 cm = 20 cm2
c) P= ((a+b)•h)•1/2= ((5+6)•4)•1/2=(11•4)•1/2=44•1/2= 22 cm2