A salt water ratio of salt to water is 1:3, then add 15 kg of salt, the ratio of salt to water is 8:15. How many kilograms of salt is there in the original brine?
一种盐水原来盐与水的比是1：3，再加入盐15千克，则盐与水的比是8：15．原来盐水中有盐多少千克？
<gadget id="calculator">8 / 15</gadget>
<output>8/15 = around 0.533333</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(8/15) - (1/3)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 / (1/5)</gadget>
<output>75</output>

<gadget id="calculator">75 * (1/3)</gadget>
<output>25</output>

<result>25</result>