Answer
(a) 33 J
(b) 8500 W
Work Step by Step
(a) Given: Capacitance $C=850\,\mu F,$ Potential difference $V=280\,V$
Recall: Energy $E=\frac{1}{2}CV^{2}$
Result: $E=\frac{1}{2}\times850\times10^{-6}\,F\times(280\,V)^{2}=33\,J$
(b) Given/known: $E=33\,J,$ Time $t=3.9\times10^{-3}\,s$
Recall: $Wattage=\frac{E}{t}$
Result: $Wattage=\frac{33\,J}{3.9\times10^{-3\,}s}=8500\,W$
