a
1
0
b
9
c
-
3
l
=
1
2
0
(
-
9
-
2
0
1
)
m
=
1
2
0
(
-
9
+
2
0
1
)
l
+
m
=
-
9
1
0
l
m
=
-
3
1
0
1
l
m
=
-
1
0
3
l
m
+
m
l
=
-
4
7
1
0