We have the functions

if we graph the functions in the interval [0,5] we have
Now that we have the graphs we can se that they are linear, we also notice that they have the same rate of change (since they are parallel). The initial value of the function y=2x+1 is 1, whereas the initial value of the function y=2x-4 is -4. We also see that the slopes of each of the functions is 2. We can conclude all if we remember that a line written in the slope-intercept form is

where m is the slope (or rate of change) and b is the intercept with the y-axis (the initial value in this case).
If we also graph the function y=2x-3 we have
We see that this function is also linear and that it has the same rate of change with the other two, whereas its initial value is -3.