A right-angled trapezoid has a lower base of 7 cm and a waist length of 5 cm. If the lower base is reduced by 4 cm, it becomes a square. What is the perimeter of the trapezoid in cm?
一个直角梯形，下底7厘米，腰长5厘米，如果下底减少4厘米，就变成正方形，这个梯形的周长是多少厘米．
<gadget id="calculator">7 - 4</gadget>
<output>3</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">7 + 6 + 5</gadget>
<output>18</output>

<result>18</result>