The value of x in 7x=63 and □+x=51 is the same, what is the number in □.
7x=63和□+x=51中x的值相同，□里的数是多少．
<gadget id="calculator">63 / 7</gadget>
<output>9</output>

<gadget id="calculator">51 - 9</gadget>
<output>42</output>

<result>42</result>