The formula of the volume of a rectangular prism is
[tex]V=l\times w\times h[/tex]where l is the length w is the width and h is the height
for a.
l=5 cm
w=7 cm
h=8 cm
[tex]V=5\times7\times8=280\operatorname{cm}^3[/tex]for b.
l=7 cm
w=7 cm
h=7 cm
[tex]V=7\times7\times7=343\operatorname{cm}^3[/tex]for c.
l=4.2 cm
w=3.6 cm
h=8.3 cm
[tex]V=4.2\times3.6\times8.3=125.496\operatorname{cm}^3[/tex]