The monthly income ratio of father and mother is 5:4. If the total monthly income of the two of them is 18,000 yuan, what is the monthly income of mother?
爸爸和妈妈的月收入之比是5：4，如果他们两人每月的总收入是18000元，那么妈妈的月收入为多少元．
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">18_000 * (4/9)</gadget>
<output>8_000</output>

<result>8_000</result>