9 9/28- (4 5/21- х)= 6 2/7
9 9/28-4 5/21+х=6 2/7 х=6 2/7-9 9/28+4 5/21 х=44/7-261/28+89/21 х=528/84-783/84+356/84 х=101/84 х=1 17/84