Agrocery store sells three different quantities of sugar. a 1 pound bag cost $1.10, a 2pound bag cost $1.98, and a three pound bag is $2.85. describe how the unit cost changes as the quantity of sugar increases.

Unit cost is cost of 1 unit of a product, here its cost of 1 pound of sugar. 
In first case unit cost is $1.10.
In second case cost of 2 pound = $1.98, or cost of 1 pound = [1.98/2] = $0.99. 
In third case cost 3 pound = $2.85, or cost of 1 pound = [2.85/3] = $0.95. 
We can see that as the quantity is increasing unit cost is decreasing.