20+50

(a)  

200+500

(a)  

7-2

(a)  

70-20

(a)  

700-200

(a)  

6+3

(a)  

60+30

(a)  

600+300

(a)  

9-6

(a)  

90-60

(a)  

900-600

(a)  

3+5

(a)  

30+50

(a)  

300+500

(a)  

8-5

(a)  

80-50

(a)  

800-500

(a)  

6+6

(a)  

60+60

(a)