STEP 1: find radius $ r $
To find radius $ r $ use formula:
$$ d = 2 \cdot r $$After substituting $ d = 12 $ we have:
$$ 12 = 2 \cdot r $$ $$ r = \dfrac{ 12 }{ 2 } $$ $$ r = 6 $$STEP 2: find volume $ V $
To find volume $ V $ use formula:
$$ V = \dfrac{ r ^{ 2 } \cdot h \cdot \pi}{ 3 } $$After substituting $ r = 6 $ and $ h = 18 $ we have:
$$ V = \dfrac{ 36 \cdot 18 \cdot \pi}{ 3 }$$$$ V = \dfrac{ 648 \, \pi}{ 3 } $$$$ V = 216\pi $$