JavaScript (ES6), 28 23 bytes
Saved 3 bytes thanks to @Mukundan314
Expects (A)(n).
A=>n=>eval(A.join`*n+`)
Try it online!
How?
We simply join the input array with "*n+", so that [1,2,3] is turned into "1*n+2*n+3" and evaluate the resulting string.
I must make it clear to you that the Earthlings will not give up so easily. I will resist. So will Lyxal. (@Lyxal, you'll fight for your glorious motherland with me, won't you? Together, our valiance shall go hard upon this cunning demigod who disrespects our Earth with his twisted ambitions.)