(x+3/4)x=12,变成(4x+3)x=48,4x^2+3x-48=0,wujie.
x-2/3=12,x=2/3+12=12(2/3);
4/9x-3=13,4/9x=3+13=16,x=16/(4/9)=16*(9/4)=36;