STEP 1: find radius $ r $
To find radius $ r $ use formula:
$$ d = 2 \cdot r $$After substituting $ d = \frac{ 15 }{ 2 } $ we have:
$$ \frac{ 15 }{ 2 } = 2 \cdot r $$ $$ r = \dfrac{ \frac{ 15 }{ 2 } }{ 2 } $$ $$ r = \frac{ 15 }{ 4 } $$STEP 2: find circumference $ C $
To find circumference $ C $ use formula:
$$ C = 2 \cdot r \cdot \pi $$After substituting $ r = \frac{ 15 }{ 4 } $ we have:
$$ C = 2 \cdot \frac{ 15 }{ 4 } \cdot \pi $$ $$ C = \frac{ 15 }{ 2 }\pi $$