x
=
e
t
(
C
1
+
C
2
t
) +
e
-
t
(
C
3
+
C
4
t
)
-
23
,
y
=
e
t
(
C
2
-
C
1
-
C
2
t
)
-
e
-
t
(
C
3
+
C
4
+
C
4
t
) + 18
.