If two squares with a side length of 15 cm are used to form a rectangle, what is the perimeter of the rectangle?
用边长为15厘米的两个正方形拼成一个长方形，求长方形的周长？
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">30 + 15</gadget>
<output>45</output>

<gadget id="calculator">45 * 2</gadget>
<output>90</output>

<result>90</result>