$C=\frac{Q}{V}=\frac{36\mu C}{1200V}=0/03\mu F=30nF$ $U=\frac{1}{2}C{{V}^{2}}=\frac{1}{2}\times (30\times {{10}^{-9}})\times (2\times {{10}^{3}})=60\times {{10}^{-3}}J=60mJ$