The volume of rectangular prism is the product of its length, width and height.
So the volume V of prism with length [tex]1 \frac{1}{4} [/tex] yards, width [tex]2 \frac{1}{2} [/tex] yards and height of 4 yards will be:
[tex]V=1 \frac{1}{4} * 2 \frac{1}{2} *4 \\ \\
V= \frac{5}{4}* \frac{5}{2}*4 \\ \\
V= \frac{25}{2} \\ \\
V=12 \frac{1}{2} [/tex]
Thus the volume of prism as a mixed number in simplest form will be [tex]12 \frac{1}{2} [/tex] cubic yards