The side lengths of a triangle are a meter, b meter and c meter. Write down the formula for calculating the perimeter of the triangle (perimeter C). If a=7, b=8, c=3, substitute the formula to calculate the perimeter of the triangle.
一个三角形的边长为a米，b米和c米，写出计算三角形周长的公式(周长C)．如果a=7，b=8，c=3，代人公式计算三角形的周长．
<gadget id="calculator">7 + 8 + 3</gadget>
<output>18</output>

<result>18</result>