v
=
v
′
+
v
1
=
63
k
m
/
h
+
12
k
m
/
h
=
75
k
m
/
h
v
=
v
′
+
v
1
=
63
k
m
/
h
+
12
k
m
/
h
=
75
k
m
/
h
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