1 2/3-5/14+(1 3/4-1/12)-4/21

= 1 28/42-15/42+(1 9/12-1/12)-4/21 = 1 13/42+1 8/12-4/21 = 1 26/84+1 56/84-16/84 = 2 82/84 - 16/48 = 2 66/48 = 3 18/48 = 3 3/8.