A mobile company newly purchased 4800 mobile phones of various types, and sold twice as many as the rest. It is known that the remaining mobile phones are 1800, how many mobile phones are there before purchasing? (Solving problems with equations)
某移动公司新购进各类手机4800部，卖出的是剩下的2倍．已知剩下的手机是1800部，购进前存的手机有多少部？(用方程解决问题)
<gadget id="calculator">1_800 * 2</gadget>
<output>3_600</output>

<gadget id="calculator">4_800 - 3_600</gadget>
<output>1_200</output>

<gadget id="calculator">1_800 - 1_200</gadget>
<output>600</output>

<result>600</result>