The number B is 160. If you subtract 40, it is exactly 4 times the number A. Find the number A.
乙数是160，如果减去40，正好是甲数的4倍，求甲数．
<gadget id="calculator">160 - 40</gadget>
<output>120</output>

<gadget id="calculator">120 / 4</gadget>
<output>30</output>

<result>30</result>