can someone help with this

[twilit pond]

how are they doing it? i dont exactly get it

[pearl talon]

It looks like they are talking about different things (?

"sum of vectors along each of the coordinate axes"
By that, they should mean
A = (Ax, Ay, Az) or A = Ax i + Ay j + Az k

I guess they mean this
A = Ax i + Ay j + Az k