c
A
l
=
880
,
m
a
t
h
r
m
f
r
a
c
J
k
g
∗
C
c
i
r
c
c
A
l
=
880
,
m
a
t
h
r
m
f
r
a
c
J
k
g
∗
C
c
i
r
c
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