a]
[tex]P=\frac{1}{2}\cdot a\cdot b\\\\a=3 \ cm\\\\b=8 \ cm\\\\P=\frac{1}{2}\cdot3\cdot8=\frac{1}{2}\cdot24=\boxed{12 \ cm^2}[/tex]
b]
[tex]P=\frac{1}{2}\cdot a\cdot h\\\\a=3 \ dm\\\\h=28 \ cm=2,8 \ dm\\\\P=\frac{1}{2}\cdot3\cdot2,8=\frac{1}{2}\cdot8,4=\boxed{4,2 \ dm^2}[/tex]
c]
[tex]P=a\cdot b\\\\a=5 \ m\\\\b=42 \ cm=0,42 \ m\\\\P=5\cdot0,42=\boxed{2,1 \ m^2}[/tex]
d]
[tex]P=a\cdot h\\\\a=14 \ dm\\\\h=0,75 \ m=75 \ cm=7,5 \ dm\\\\P=14\cdot7,5=\boxed{105 \ dm^2}[/tex]
e]
[tex]P=\frac{1}{2}\cdot(a+b)\cdot h\\\\a=8 \ cm\\\\b=12 \ cm\\\\h=10 \ cm\\\\P=\frac{1}{2}\cdot(8+12)\cdot10=20\cdot5=\boxed{100 \ cm^2}[/tex]
f]
[tex]a=48 \ cm\\\\b=2,6 \ dm=26 \ cm\\\\h=250 \ mm=25 \ cm\\\\P=\frac{1}{2}\cdot(48+26)\cdot25=\frac{1}{2}\cdot74\cdot25=37\cdot25=\boxed{925 \ cm^2}[/tex]
