How do you derive a market supply curve from individual supply curves?

The third program provides families with $50 in food stamps each week, redeemable for both perishable and nonperishable food. the fourth policy instead provides a family with a box of nonperishable foods each week, worth $50. use two graphs to illustrate that a family may be indifferent between the two programs, but will never prefer the $50 box of nonperishable foods over the $50 in food stamps. state your answer and use a consumer choice model for perishable food and nonperishable food to graphically justify your choice.