s
=
s
1
+
s
3
−
s
2
=
3
k
m
+
12
,
5
k
m
−
5
k
m
=
10
,
5
k
m
s
=
s
1
+
s
3
−
s
2
=
3
k
m
+
12
,
5
k
m
−
5
k
m
=
10
,
5
k
m