b$)$ Show that under $\frac{?}{\text{b}\text{a}\text{r}}(p),$ the discounted self$-$financing portion

$\{(1+r{)}^{-(n+1)}{x}_{n+1}{\}}_n=0^N$ in the context of

BOPM

b$)$ Show that under $\frac{?}{\text{b}\text{a}\text{r}}(p),$ the discounted self$-$financing portiono

$\{(1+r{)}^{-(n+1)}{x}_{n+1}{\}}_n=0^N.$ Justify your response with suitable workings.

$[7$ marks$]$