so hmmm check the picture below
now
[tex]\bf V=\pi 9^2\cdot \cfrac{1}{4}\implies V=\cfrac{81\pi }{4}
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\textit{there are }27ft^3\ in\ 1yd^3\textit{ thus, let's convert them to }yd^3
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\cfrac{\frac{81\pi }{4}}{27}\iff \cfrac{\frac{81\pi }{4}}{\frac{27}{1}}\implies \cfrac{81\pi }{4}\cdot \cfrac{1}{27}\implies \boxed{\cfrac{3\pi }{4}}[/tex]
now, that's how many yard³ are there for that slab, now, how much is the cost?
well, each yd³ costs $40, thus [tex]\bf 40\cdot \cfrac{3\pi }{4}[/tex]
