A barrel of oil, use up (1/4), exactly 7kg left. How many kilograms is this barrel of oil?
一桶油，用去(1/4)，正好剩7kg．这桶油有多少千克？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">7 / (3/4)</gadget>
<output>28/3 = around 9.333333</output>

<result>28/3 = around 9.333333</result>