(1/6 - 5/9 )*(1/2 - 3/7)*7 1/5
1/6-5/9=3/18-10/18=-7/18
1/2-3/7=7/14-6/14=1/14
-7/18*1/14=-1/36
-1/36*7 1/5=-1/36*36/5=-1/5