STEP 1: find height $ h $
To find height $ h $ use formula:
$$ h = 2 \cdot r $$After substituting $ r = 10 $ we have:
$$ h = 2 \cdot 10 $$ $$ h = 20 $$STEP 2: find side $ a $
To find side $ a $ use formula:
$$ A = a \cdot h $$After substituting $ A = 480 $ and $ h = 20 $ we have:
$$ 480 = 20 \cdot a $$$$ a = \dfrac{ 480}{ 20 } $$$$ a = 24 $$