9 5/28-(7 1/7-х)=2 4/21
9 5/28-7 1/7+х=2 4/21
Х=2 4/21+7 1/7-9 5/28
Х=2 16/84+7 12/84-9 15/84
Х=13/84
9 5/28-(7 1/7-х)=2 4/21
9 5/28-7 1/7+х=2 4/21
Х=2 4/21+7 1/7-9 5/28
Х=2 16/84+7 12/84-9 15/84
Х=13/84