Use a 3.6-meter-long wooden bar to make a fly-proof frame with a length of 40 cm and a width of 30 cm. What is the height of the fly guard?
用一根长3.6米的木条做一个长40厘米，宽30厘米的防蝇罩框架．防蝇罩的高是多少厘米？
<gadget id="calculator">3.6 * 100</gadget>
<output>360</output>

<gadget id="calculator">360 / 4</gadget>
<output>90</output>

<gadget id="calculator">40 + 30</gadget>
<output>70</output>

<gadget id="calculator">90 - 70</gadget>
<output>20</output>

<result>20</result>