There is a triangular signboard with a height of 7.8 decimeters and a bottom of 9 decimeters. The price of materials per square meter is 90 yuan. How much does it cost to make 100 signs like this?
有一块三角形标志牌，高是7.8分米，底是9分米．每平方米材料的价格是90元，做100块这样的标志牌，需要多少钱？
<gadget id="calculator">9 / 2 / 100</gadget>
<output>9/200 = around 0.045</output>

<gadget id="calculator">7.8 * (9/200) * 90 * 100</gadget>
<output>3_159</output>

<result>3_159</result>