Please refer to the attached image.
-2/5, 4/5 and -2/5 + 4/5 have been marked in red in the image
The points marked on the number line are separated by a distance of 1/5.
So when you add 4/5 to -2/5 you need to move 1/5 4 times (4/5 = 4 x 1/5) towards the right to reach the SUM.
Based on this, the sum of -2/5 and 4/5 is 2/5, and has been highlighted in the image.
