2/3-z=0.4
2/3-z=4/10
2/3-z=2/5
2/3-2/5=z
10/15-6/15=z
4/15=z
4/7+t=0.7
4/7+t=7/10
t=7/10-4/7
t=49/70-40/70
t=9/70
2/3-z=0.4
2/3-z=4/10
2/3-z=2/5
2/3-2/5=z
10/15-6/15=z
4/15=z
4/7+t=0.7
4/7+t=7/10
t=7/10-4/7
t=49/70-40/70
t=9/70
z=2/3-4/10
z=2/3-2/5
z=10/15-6/15
z=4/15
б)t=0,7-4/7
t=7/10-4/7
t=49/70-40/70
t=9/70