P$4.$ The voltage across a capacitor is described by $=50$ V$,$ t $0100+600$ V$,0$ If the capacitor is valued at $4$mF and has a current $0+=2$A$,$ find: $($a$)$ The constants A and B$,($b$)$ The energy stored in the capacitor at $=0.($c$)$ The capacitor current for all $>0.$