计算下列平行四边形的面积。
①$a=8\ \mathrm{m},h=0.7\ \mathrm{m}$
$S=ah⇒ S=(\ \ \ \ )\mathrm{m}^2$
②$a=5.2\ \mathrm{dm},h=0.5\ \mathrm{dm}$
$S=$
③$a=3.2\ \mathrm{cm},h=2\ \mathrm{cm}$
$S=$
④$a=12\ \mathrm{m},h=9\ \mathrm{m}$
$S=$
⑤$a=0.5\ \mathrm{dm},h=0.5\ \mathrm{dm}$
$S=$
⑥$a=3.9\ \mathrm{cm},h=20\ \mathrm{cm}$
$S=$
⑦$a=2.36\ \mathrm{dm},h=10\ \mathrm{dm}$
$S=$
⑧$a=56\ \mathrm{m},h=101\ \mathrm{m}$
$S=$
⑨$a=8.6\ \mathrm{cm},h=0.3\ \mathrm{cm}$
$S=$
⑩$a=2.3\ \mathrm{cm},h=1.2\ \mathrm{cm}$
$S=$
⑪$a=10\ \mathrm{m},h=0.8\ \mathrm{m}$
$S=$
⑫$a=1.1\ \mathrm{cm},h=1.8\ \mathrm{cm}$
$S=$
⑬$a=4\ \mathrm{m},h=3.2\ \mathrm{m}$
$S=$
⑭$a=21\ \mathrm{cm},h=6\ \mathrm{cm}$
$S=$
⑮$a=0.8\ \mathrm{dm},h=7.8\ \mathrm{dm}$
$S=$
⑯$a=12\ \mathrm{m},h=30\ \mathrm{m}$
$S=$
⑰$a=0.2\ \mathrm{cm},h=69\ \mathrm{cm}$
$S=$
⑱$a=0.75\ \mathrm{dm},h=2\ \mathrm{dm}$
$S=$
⑲$a=42\ \mathrm{cm},h=5\ \mathrm{cm}$
$S=$
⑳$a=1.5\ \mathrm{cm},h=40\ \mathrm{cm}$
$S=$

① $S=ah⇒ S=5.6\ \mathrm{m}^2$
② $S=5.2×0.5=2.6\ \mathrm{dm}^2$
③ $S=3.2×2=6.4\ \mathrm{cm}^2$
④ $S=12×9=108\ \mathrm{m}^2$
⑤ $S=0.5×0.5=0.25\ \mathrm{dm}^2$
⑥ $S=3.9×20=78\ \mathrm{cm}^2$
⑦ $S=2.36×10=23.6\ \mathrm{dm}^2$
⑧ $S=56×101=5656\ \mathrm{m}^2$
⑨ $S=8.6×0.3=2.58\ \mathrm{cm}^2$
⑩ $S=2.3×1.2=2.76\ \mathrm{cm}^2$
⑪ $S=10×0.8=8\ \mathrm{m}^2$
⑫ $S=1.1×1.8=1.98\ \mathrm{cm}^2$
⑬ $S=4×3.2=12.8\ \mathrm{m}^2$
⑭ $S=21×6=126\ \mathrm{cm}^2$
⑮ $S=0.8×7.8=6.24\ \mathrm{dm}^2$
⑯ $S=12×30=360\ \mathrm{m}^2$
⑰ $S=0.2×69=13.8\ \mathrm{cm}^2$
⑱ $S=0.75×2=1.5\ \mathrm{dm}^2$
⑲ $S=42×5=210\ \mathrm{cm}^2$
⑳ $S=1.5×40=60\ \mathrm{cm}^2$