（-24）x(-1/2-1/3+1/4)
=24x1/2+24x1/3-24x1/4
=12+8-6
=14
（-24）x(-1/2-1/3+1/4)
=24x(1/2+1/3-1/4)
=24x(6/12+4/12-3/12)
=24x7/12
=14