In our simple urban model U(s)=u(x(s),q(s)),and the budget constraint X(s)+r(s)q(s)+c(s)=y

a) Explain the steps necessary to derive the compensated demand functions x(r(s),U) and q(r(s),U) for an individual located at a given s (Note:you can derive then if you wish but all I am asking for is a good description of the steps)

b)How do we go from x(r(s),U) and q(r(s),U) to minimum expenditure function y(r(s),c(s),U)?

c) what condition will hold (other than constraint) if the individual has maximized its utility subject to its budget constraint (or minimized its expenditure subject to a given level of utility) at a given location s