Giải giúp em bài 2 bài 3

Bài 2:

$\begin{array}{l}
2m8dm=20dm+8dm=28dm\\
8km6m=8000m+6m=8006m\\
7500m=7km500m\\
6m42cm=600cm+42cm=642cm\\
7m3dm=700cm+30cm=730cm\\
9km=9000m
\end{array}$

Bài 3:

$\begin{array}{l}
a)\,21049+10999×5\\
=21049+54995\\
=76044\\
b)\,328-(125-38)\\
=328-87\\
=241
\end{array}$