Situations
Budget Constraint Line
1) Never Using Coupons
P x ( 1 + τ + t + τ t ) ⋅ X + P y Y = M
2) Using Coupons
P x ( 1 − ϕ + τ + t + τ t ) ⋅ X + P y ⋅ Y = M
3) Coupons Unavailable after Being Available
P x ( 1 + τ + t + τ t ) ⋅ X + P y ⋅ Y = M − Ω