A trapezoidal publicity board has an upper base of 4 meters, a lower base of 5 meters, and a height of 6 meters. The front and back of the sign were painted with 810 kilograms of cement. How many kilograms of cement was used on average per square meter?
一块梯形宣传牌，上底是4米，下底是5米，高是6米，用810千克的水泥粉刷了这面牌子的正反面，平均每平方米用水泥多少千克？
<gadget id="calculator">4 + 5</gadget>
<output>9</output>

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

<gadget id="calculator">9 * 3</gadget>
<output>27</output>

<gadget id="calculator">810 / 27</gadget>
<output>30</output>

<result>30</result>