I'm not sure how you got c but the way you would solve this is for every x on the line plot you would add that amount. You don't need to worry about 0 because 0 is nothing.
There are 3 X's at 1/4 so you would add 1/4+1/4+1/4=3/4. There are 2 X's at 1/2 so you would add 1/2+1/2=1. There are 2 X's at 3/4 so you would add 3/4+3/4=1.5. There is 1 X at 1 so it would just be 1. Then add all those together 3/4+1+1.5+1=4.25 or you could just add each X as you come across it on the number line like so:
There are 3 X's at 1/4 so you would add 1/4+1/4+1/4=3/4. There are 2 X's at 1/2 so you would add 1/2+1/2=1. There are 2 X's at 3/4 so you would add 3/4+3/4=1.5. There is 1 X at 1 so it would just be 1. Then add all those together 3/4+1+1.5+1=4.25 or you could just add each X as you come across it on the number line like so: