Hi This is concerning the standard trade model
so,
Qc= quantity of cloth
Qf= quantity of food
Pc= price of cloth
Pf= price of food
V=aQc^2+Qf^2 is the PPF or TT
V=PcQc+PfQf is isovalue line
U= Dc^(1/2)*Df^(1/2)
find optimal Qc and Qf from isovalue line and PPF