Kibble book exercise about conservative forces

Kibble book exercise 1, chapter 3. It is the following:

Find which of the following forces are conservative, and, for those that are conservative, determine the corresponding potential energy function (a and b are constants, and a is a constant vector)

i) Fx = a*x + b*y^2

ii) Fx= a*y

vi) F= a *(a*r)