Plotting a dashed line onto a graph

So here's my graph:

How do I add a dashed line that originates from a particular point somewhere in the middle of the plot on each of the graphs? For example, I would like my dashed line to start at the point 3 on the x-axis for the green curve on the bottom of the second graph and will terminate at point 5

Observe the following graph I'm trying to replicate, notice the dashed lines originating from a particular point on each of the graphs then terminates at the end. I'm not recreating parts b. and d. like this graph has it so not worried about dashed lines extending beyond the the end of the axis for parts a. and c.

Answer 1

[M.B]

add this to your plot:

x_from = 3;% the dotted line starts at x = 3
x_to = 5;% the dotted line finished at x = 5
yvalue = 2.3;% the line will have an amplitude of 2.3
plot([3 5], [yvalue yvalue], 'b:');% b for blue, r for red, g for green , k for black ...