(a) By using number line, it is clear that:

9 + (-6)

= 9 – 6

= 3

(b) By using number line, it is clear that:

5 + (- 11)

= 5 – 11

= - 6

(c) By using number line, it is clear that:

(-1) + (-7)

= - 1 – 7

= - 8

(d) By using number line, it is clear that:

(- 5) + 10

= 5

(e) By using number line, it is clear that:

(-1) + (-2) + (-3)

= - 1 – 2 – 3

= - 6

(f) By using number line, it is clear that:

(- 2) + 8 + (- 4)

= -2 + 8 – 4

= - 6 + 8

= 2