How many kilograms of water are added to 15 kilograms of salt to obtain a salt water with a salt content of 30%.
往15千克盐中加入多少千克水，可得到含盐率为30%的盐水．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">15 / (3/10)</gadget>
<output>50</output>

<gadget id="calculator">50 - 15</gadget>
<output>35</output>

<result>35</result>