A triangular billboard with a base of 12m and a height of 4.2m. If you want to paint it again, you need 0.7 kilograms of paint per square meter. At least how many kilograms of paint is needed?
一块三角形广告牌，底是12m，高是4.2m．如果要用油漆刷一遍，每平方米需要油漆0.7千克．至少需要多少千克油漆？
<gadget id="calculator">4.2 / 2</gadget>
<output>2.1</output>

<gadget id="calculator">12 * 2.1 * 0.7</gadget>
<output>17.64</output>

<result>17.64</result>