The formula to find the volume of a right trapezoidal prism is
[tex]\begin{gathered} V=\frac{(a+b)}{2}\cdot h\cdot l \\ \text{ Where V is the volume} \\ a\text{ is the long base} \\ \text{b is the short base} \\ h\text{ is the height and } \\ l\text{ is the length of the right trapezoidal prism} \end{gathered}[/tex]So, in this case, you have
[tex]\begin{gathered} a=7.5in \\ b=5in \\ h=6in \\ l=8in \end{gathered}[/tex][tex]\begin{gathered} V=\frac{(a+b)}{2}\cdot h\cdot l \\ V=\frac{(7.5in+5in)}{2}\cdot6in\cdot8in \\ V=300in^3 \end{gathered}[/tex]Therefore, the volume of the right trapezoidal prism is 300 cubic inches.