When multiplying two numbers, if one factor increases by 4, the product increases by 64, and if the other factor decreases by 7, the product decreases by 140. What is the product of the two numbers.
两个数相乘，如果一个因数增加4，积就增加64，如果另一个因数减少7，积就减少140．原来两个数的积是多少．
<gadget id="calculator">64 / 4</gadget>
<output>16</output>

<gadget id="calculator">140 / 7</gadget>
<output>20</output>

<gadget id="calculator">16 * 20</gadget>
<output>320</output>

<result>320</result>