A piece of triangular glass has a base of 12.5 decimeters and a height of 7.8 decimeters. If the price per square decimeter of glass is 0.8 yuan, how much will it cost to buy this piece of glass?
一块三角形的玻璃，底12.5分米，高是7.8分米，如果每平方分米玻璃的价钱是0.8元，买这块玻璃要用多少钱？
<gadget id="calculator">7.8 / 2</gadget>
<output>3.9</output>

<gadget id="calculator">12.5 * 3.9</gadget>
<output>48.75</output>

<gadget id="calculator">48.75 * 0.8</gadget>
<output>39</output>

<result>39</result>