Master Zhang has two planks of the same width, one is 120 cm long and the other is 150 cm long. He overlapped one end of two planks together to form a long plank. The overlapping part is 30 centimeters. How many centimeters is the long plank after overlapping.
张师傅有两块一样宽的木板，一块长120厘米，一块长150厘米．他把两块木板的一端重叠在一起，成为一块长木板，重叠部分是30厘米，重叠后的长木板长多少厘米．
<gadget id="calculator">150 - 30</gadget>
<output>120</output>

<gadget id="calculator">120 + 120</gadget>
<output>240</output>

<result>240</result>