A=1/3-1/3×4/7
=1/3-4/21
=(7-4)/21
=3/21
=(3÷3)/(21÷3)
=1/7
B=6/5÷(1/15-1/5)
=6/5÷(1-3)/15
=6/5÷(-2/15)
=6/5×(-15/2)
=-90/10
=-(90÷10)/(10÷10)
=-9
