$(5$ points$)$ The following information is available for Switzerland and the United States:

$\backslash$table$[[,1970,1990,2014],[$Consumer price index $($Switzerland$,2010=100),33\mathrm{.}4,75\mathrm{.}7,99\mathrm{.}3],[$Official exchange rate $($CHF$/$USD$),$CHF$4\mathrm{.}44/$$$,$CHF$1\mathrm{.}39/$$$,$CHF$0\mathrm{.}92/$$$],[$Consumer price index $($USA$,2010=100),17\mathrm{.}8,59\mathrm{.}9,108\mathrm{.}6]]$

Estimate change in relative purchasing parity for Swiss Franc $($CHF$)$ in $1970-1990$ and $1990-2014.$ Is current level of exchange rates $)=(CHF\frac{0\mathrm{.}92}{\text{\$}}$ sustainable based on your estimate?