Step 1: Marketable surplus is the quantity of produce left for sale after the farm family keeps back what it needs for its own consumption, seed, and other farm uses.
Step 2: A larger family size means more of the produce is kept back for household consumption, which reduces the amount left to sell, so this relationship is negative.
Step 3: A larger holding size, better quality of produce, and greater resources all raise total output, which increases the surplus available for sale, so these three have a positive relationship.