X(X+3)分之1+(X+3)(X+6)分之1+(x+6)(X+9)分之1=2(X+9)分之3
3{1/x-1/(x+3)+1/(x+3)-1/(x+6)+1/(x+6)-1/(x+9)}=3/(2(x+9)
3{1/x-1/(x+9)=3/2(x+9)
3*8/x(x+9)=3/2(x+9)
x=16