How many four-digit numbers composed of the four numbers 5, 6, 7, and 8 are divisible by 2?
由5、6、7、8这四个数组成的能被2整除的四位数共有多少个．
<gadget id="calculator">2 * 3 * 2 * 1</gadget>
<output>12</output>

<result>12</result>