If `vec(a) = 3hat(i) - hat(j)` and `vec(b) = 2hat(i) + hat(j) - 3hat(k)` then express `vec(b)` in the form of `vec(b) = vec(b_(1)) + vec(b_(2))` where `vec(b_(1))||vec(a)` and `vec(b_(2))` perpendicular to `vec(a)`.