piece of iron wire surrounds a rectangle with a length of 8 cm and a width of 7 cm, and there is 4 cm left. How much longer is the iron wire than the original one?
一根铁丝围了一个长8厘米、宽7厘米的长方形，还剩4厘米，这根铁比原来长多少厘米．
<gadget id="calculator">8 + 7</gadget>
<output>15</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">30 + 4</gadget>
<output>34</output>

<result>34</result>