1)
Why does it say twice "va'Yochal"?
1.
Malbim: Arbeh ate the grass, and Yelek ate Pri ha'Adamah that grow in the ground; Arbeh do not eat them.
2)
What are "Pri Adamasam"?
1.
Radak: They are tree fruits that the hail left over.
2.
Malbim: They are Pri ha'Adamah that grow in the ground.