If the number of terms in the expansion of $\bigg(1- \large\frac{2}{x}+\frac{4}{x^2}\bigg)^n,x \neq 0,$ is 28, then the sum of the coefficients of all the terms in this expansion, is

Question

$\begin{array}{1 1}(1) 64 \\(2) 2187 \\ (3) 243\\ (4) 729 \end{array} $