Explanation:
it is basically simple.
the slope is the ratio (y coordinate difference / x coordinate difference) when going from one point on the line to another.
in other words : when x changes a certain amount of units, how many units does then y change.
so, from e.g. (2, 1) to (6, 12) we see
x changes by +4 (from 2 to 6).
y charges by +11 (from 1 to 12).
so, the slope is +11/+4 = 11/4.
the same ratio applies to all the other point intervals in the table.
e.g. (10, 23) to (14, 34)
+4 (10 to 14)
+11 (23 to 34)
and so on.
so, the slope truly is 11/4.