Problem DTFT X(e^jw)

I need help this question.

 x(n)=2(0.8)^n[u(n)-u(n-20)]

Sugestions functions?

[Youssef Khmou]

explain exactly what is the issue, what are n x ?

Answer 1

[Yao Li]

x(n)=2*((0.8)^n)*(u(n)-u(n-20));

I'm not sure whether it is what you want.