Let f$($t$)=8$$($t$)+6\mathrm{.}7$u$($t$)+6\mathrm{.}8$t$2$u$($t$).$

Then in s$-$domain we have $.$

What is the value of C$?$

Use V$1($t$)$ as the unknown signal, the KCL equation of the above circuit is

$.$

What is the value of X$?$