10

20

30

10

20

40

10

20

30

70 - 30 = 40

70 - 40 = 30

30 + 40 = 70

70

60

80

20

30

40

40

50

60

40 - 10 = 30

40 - 30 = 10

10 + 40 = 50

60

70

80