a)
[tex]a = 8 \ cm\\h = 4 \ cm\\\\P = a\cdot h = 8 \ cm\cdot4 \ cm =\boxed{32 \ cm^{2}}[/tex]
b)
[tex]d_1 = 10 \ cm\\d_2 = 6 \ cm\\\\P = \frac{1}{2}d_1\cdot d_2 = \frac{1}{2}\cdot10 \ cm\cdot6 \ cm = \boxed{30 \ cm^{2}}[/tex]
c)
[tex]a = 4 \ cm + 2 \ cm = 6 \ cm\\b = 4 \ cm\\h = 3 \ cm\\\\P = \frac{a+b}{2}\cdot h=\frac{6 \ cm+4 \ cm}{2}\cdot3 \ cm = 5 \ cm\cdot 3 \ cm =\boxed{ 15 \ cm^{2}}[/tex]
