100 grams of salt water with a concentration of 20% is added to the salt water with a concentration of 30% after adding the same quality of salt and water. May I ask: how many grams of salt are added?
现有浓度为20%的盐水100克，加入相同质量的盐和水后，变成了浓度为30%的盐水，请问：加了多少克盐？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">100 * (1/5)</gadget>
<output>20</output>

<gadget id="calculator">100 - 20</gadget>
<output>80</output>

<gadget id="calculator">80 - 20</gadget>
<output>60</output>

<gadget id="calculator">70 - 30</gadget>
<output>40</output>

<gadget id="calculator">60 / 40</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(3/2) * 30</gadget>
<output>45</output>

<gadget id="calculator">45 - 20</gadget>
<output>25</output>

<result>25</result>