In the ratio 3:10=18:60, if the second item increases its (1/2), how much must the fourth item increase, and the ratio still holds.
在比例3：10=18：60中，如果第二项增加它的(1/2)，那么第四项必须增加多少，比例仍然成立．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">10 * (1/2)</gadget>
<output>5</output>

<gadget id="calculator">10 + 5</gadget>
<output>15</output>

<gadget id="calculator">18 / 3</gadget>
<output>6</output>

<gadget id="calculator">15 * 6</gadget>
<output>90</output>

<gadget id="calculator">90 - 60</gadget>
<output>30</output>

<result>30</result>