We have three functions:
FIRST.

The slope of f(x) is 2
SECOND.
g(x) graph going through (0, -5) and (4, 3), so:
We can find the slope of g(x) as follows:

The slope of g(x) is 2
THIRD.
h(x) passes through (-1, 3), (1, 7) and (3, 11)
We can find the slope of h(x) as follows:

The slope of h(x) is 2
So, it is obvious that the three functions have the same slope 2.