D$5\mathrm{.}1.$ Given the vector current density J $=10$p$2$za$,-4$p cos$^2$ a mA$/$m$^2$: $($a$)$ find the current density at P$($p $=3,4=30\backslash$deg $,$ z $=2)$; $($b$)$ determine the total current flowing outward through the circular band p $=3,0<<2.2$