6

7

8

9

(a)  

6

7

5

4

(a)  

6

7

5

-4

(a)  

9

4

8

7

(a)  

6

4

8

9

(a)  

8

4

1

6

(a)  

5

9

-4

7

(a)  

5

8

-6

4

(a)  

6

7

5

8

(a)  

8

9

4

6

(a)  

5

6

9

-8

(a)  

6

4

8

9

(a)  

5

8

6

-3

(a)  

6

4

9

3

(a)