6*(5+4+3+2-1)=78
(2-1)*(3+4+5)*6/6*(5+4+3+2-1)/5x4x3+6x(1+2)=78/5*6*3-(1+2)*4等
6x(1+2)+5x4x3=78
6*(5+4+3+2-1)
5 5x4x3+6x[1+2]=78