3,8+х = 1 4/5
3,8 = 3 8/10 = 3 4/5
3 4/5+х = 1 4/5
х = 1 4/5 - 3 4/5
х = -2
проверка: 3,8+(-2) = 1 4/5 ; 1,8 = 1,8
5 2/7 + = - 3 9/14
37/7+х = -51/14
х = -51/14-37/7
х= (-51-74)/14
х = -125/14= -8 13/14
проверка
5 2/7 +(-8 13/14) = -3 9/14
74/14-125/14 = -51/14
-51/14 = -51/14