12/(x-6)*10/3-9 = 1981-1900 =81
12/(x-6)*10/3 = 81+9=90
12/(x-6) = 90 * 3/10 = 27
x-6 = 12/27 =4/9
x = 6又9分之4 = 58/9
解方程：[12除以（x-6）*3又3分之1-9]+1900=1981
12/(x-6)*10/3-9 = 1981-1900 =81
12/(x-6)*10/3 = 81+9=90
12/(x-6) = 90 * 3/10 = 27
x-6 = 12/27 =4/9
x = 6又9分之4 = 58/9