У - 13/51 = - 9/34
у = - 9/34 + 13/51
у = - 27/102 + 26/102
y = - 1/102
----------------------------------
2/3 - z = 0,4
2/3 - z = 4/10
2/3 - z = 2/5
z = 2/3 - 2/5
z = 10/15 - 6/15
z = 4/15
----------------------------------
4/7 + t = 7/10
t = 7/10 - 4/7
t = 49/70 - 40/70
t = 9/70