The existing concentration of 20% saline solution is 45 grams. To turn it into a liquid medicine with a concentration of 40%, how many grams should be added?
现有浓度为20%的盐水溶液45克，要将它变成浓度为40%的药水，需要加药多少克？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(4/5) / (3/5)</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">45 * (4/3)</gadget>
<output>60</output>

<gadget id="calculator">60 - 45</gadget>
<output>15</output>

<result>15</result>