e = 5cm
f = 5cm + 7,5cm = 12 [tex]\frac{1}{2}[/tex] cm
P = [tex]\frac{e*f}{2}[/tex] = [tex]\frac{5*12\frac{1}{2} }{2}[/tex] = [tex]\frac{62\frac{1}{2} }{2}[/tex] = [tex]\frac{125}{2} * \frac{1}{2}[/tex] = [tex]\frac{125}{4}[/tex] [tex]cm^{2}[/tex]
P = 31 [tex]\frac{1}{4}[/tex] [tex]cm^{2}[/tex]
