4x + 0.5x = 4.5×0.8(4 + 0.5)x = 4.5×0.84.5x = 4.5×0.8x = 0.8设这个数为 x ,则6x - 2x = 3.2(6 - 2)x = 3.24x = 3.2x = 3.2÷4x = 0.8 梯形面积 = (上底 + 下底)×高 ÷ 2 = 中位线×高