Does this help you to conclude anything about the linear equation $y = ax + b$ when $a$ is fixed but $b$ varies (Refer to Fig 2.13 in NCERT page no. 34)?                                                                                                                  [Page No. 35]

All three lines have the same slope (2), so they are parallel to each other equally steep, never meeting.

Changing $b$ simply slides the line up or down without tilting it.
Each line cuts the $y$-axis at $(0, b)$: $y = 2x - 1$ at $(0, -1)$, $y = 2x + 1$ at $(0, 1)$, and $y = 2x + 5$ at $(0, 5)$.