If the value of 4x+18 is 42, what is the value of 15x-18?
如果4x+18的值是42，那么15x-18的值是多少．
<gadget id="calculator">42 - 18</gadget>
<output>24</output>

<gadget id="calculator">24 / 4</gadget>
<output>6</output>

<gadget id="calculator">15 * 6</gadget>
<output>90</output>

<gadget id="calculator">90 - 18</gadget>
<output>72</output>

<result>72</result>