原式=（3/4-3/16)x(2/9+1/3)
=3/4x2/9+3/4x1/3-3/16x2/9-3/16x1/3
=1/6+1/4-1/24-1/16
=8/48+12/48-2/48-3/48
=15/48
=5/12