Answer:

Explanation:
To add these vectors together, we have to "glue" them together.
Let's call the vector with the length of 2 A and the one with length 4 B.
Imagine you can grab vector A with your hands and move it to the end of B (it would look like the image that's annexed)
Now imagine that we made a triangle from that, what we want to know is the hypotenuse of that triangle!
We know that when we want to find the hypotenuse of a triangle, we can use Pythagoras theorem:

Let's plug in the known values (the length of the vectors) and solve this

Good luck!