The upper base of a trapezoid is acm, the lower base is 6cm longer than the upper base, the height is 12cm, and the area is 192cm**2. What is the upper base of the trapezoid in cm? (solution with equation)
一个梯形上底是acm，下底比上底长6cm，高是12cm，面积是192cm**2．梯形的上底是多少cm．(用方程解答)
<result>13</result>