Length is the absolute value of the difference between the two points. Since you have a number line, you could just count how many units there are between the two points.
#1) Using absolute value
HI = |1 - 4|
= |-3|
= 3
#1) Counting
start at H and start counting until you land on I.
H is on 1 so move one unit toward I and you land on 2.
move a second time toward I and you land on 3,
move a third time toward I and you land on 4, (which is where I is located)
You moved 3 times so the length from H to I is 3 units.
Try problems 2 and 3 on your own and then check the answers below.
2) GI = 7
3) EG = 3