from the given SDT we conclude some rules
i)' *' is least priority and left associative.
ii)'-' is 2nd highest priority and left associative
iii) '/' is highest priority and right associative.
1) 8/4*2-6*4
=2*2-6*4 (8/4=2)
=2*-4*4 (2-6=-4)
=-2*4 (2*-4=-2 addition property for *)
a1=2
2) 6*2/1-2*3
=6*2-2*3
=6*0*3
=6*3
a2=9.
so a1-a2=2-9=-7