84. а) х = 13/8 + 13/5 = (65+104)/40 = 169/40 = 4 9/40
б) у = 25/4 - 35/6 = (75-70)/12 = 5/12
87. а) х = 12 - 10/9 = (108-10)/9 = 98/9 = 10 8/9
б) х = 127/18 - 53/9 = (127-106)/18 = 21/18 = 7/6
89. а) = 47/6 - 51/8 + 34/9 = (564 - 459 + 272)/72 = 377/72 = 5 17/72
б) = 179/20 - 97/30 - 79/15 = (537 - 194 - 316)/60 = 27/60 = 9/20
в) = 271/25 - 16/5 - 47/10 = (542 - 160 - 235)/50 = 147/50 = 2 47/50
г) = 149/12 + 33/8 - 14/3 = (298 + 99 - 112)/24 = 285/24 = 11 7/8
д) = 21 - 51/8 + 13/6 = (504 - 153 + 52)/24 = 403/24 = 16 19/24
е) = 59/10 + 5 - 38/15 = (177 + 150 - 76)/30 = 251/30 = 8 11/30