For a semicircle with a radius of 1.5 cm, what is the formula for its perimeter?
半径是1.5厘米的半圆形，求它的周长列式为？
<gadget id="calculator">3.14 * 1.5</gadget>
<output>4.71</output>

<gadget id="calculator">1.5 * 2</gadget>
<output>3</output>

<gadget id="calculator">4.71 + 3</gadget>
<output>7.71</output>

<result>7.71</result>