The volume of rain that fells in the field is simply given by the area of the field, which is
[tex]A=100 mm^2[/tex]
multiplied by the height of rain that fell, which is
[tex]h=5.0 mm[/tex]
Therefore, the volume is
[tex]V=hA=(5 mm)(100 mm^2)=500 mm^3[/tex]
