(3/7-16/21)×2 1/7+(11/15+0,3):12 2/5

3/7-16/21=9/21-16/21=-7/21=-1/3-1/3*2 1/7=-1/3*15/7=-5/711/15+3/10=22/30+9/30=31/30=1 1/301 1/30:12 2/5=31/30*5/62=1/12-5/7+1/12=-60/84+7/84=-53/84