If the sum of the two-digit numbers \overline{ab} and \overline{cd} is 79, what is the maximum value of a*b*c*d?
如果两位数\overline{ab}与\overline{cd}的和是79，那么a*b*c*d的最大值是多少．
<gadget id="calculator">3 * 4 * 4 * 5</gadget>
<output>240</output>

<result>240</result>