If the same number is filled in the box of (15*□-60)/3=□, the equation can be established, then □=how much.
如果在(15*□-60)/3=□的方框内填入同一个数，能使等式成立，那么□=多少．
<gadget id="calculator">60 / 3</gadget>
<output>20</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<result>5</result>