STEP 1: find side $ a $

To find side $ a $ use formula:

$$ r = \dfrac{ a }{ 2 } $$

After substituting $r = 3\, \text{cm}$ we have:

$$ 3\, \text{cm} = \dfrac{ a }{ 2 } $$ $$ a = 3\, \text{cm} \cdot 2 $$ $$ a = 6\, \text{cm} $$

STEP 2: find base area $ B $

To find base area $ B $ use formula:

$$ B = a^2 $$

After substituting $a = 6\, \text{cm}$ we have:

$$ B = \left( 6\, \text{cm} \right)^{2} $$ $$ B = 36\, \text{cm}^2 $$

STEP 3: find lateral surface $ L $

To find lateral surface $ L $ use formula:

$$ L = 2 \cdot a \cdot s $$

After substituting $a = 6\, \text{cm}$ and $s = 5\, \text{cm}$ we have:

$$ L = 12\, \text{cm} \cdot 5\, \text{cm} $$$$ L = 60\, \text{cm}^2 $$

STEP 4: find total surface $ A $

To find total surface $ A $ use formula:

$$ A = B + L $$

After substituting $B = 36\, \text{cm}^2$ and $L = 60\, \text{cm}^2$ we have:

$$ A = 36\, \text{cm}^2 + 60\, \text{cm}^2 $$ $$ A = 36\, \text{cm}^2 + 60\, \text{cm}^2 $$ $$ A = 96\, \text{cm}^2 $$

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