20+(7 1/3 - 6 7/8):3/4 - (5 1/4 - 4 21/40): 1 9/20

20 + (7 1/3 - 6 7/8) : 3/4 - (5 1/4 - 4 21/40) : 1 9/20 = 20 + (22/3 - 55/8) : 3/4 - (21/4 - 181/40) : 29/20 = 20 + (176/24 - 165/24) : 3/4 - (210/40 - 181/40) : 29/20 = 20 + 11/24 : 3/4 - 29/40 : 29/20 = 20 + 11/24 * 4/3 - 29/40 * 20/29 = 20 + 11/18 - 1/2 = 20 + 11/18 - 9/18 = 20 + 2/18 = 20 + 1/9 = 20 1/9.