Write an equation involving two ratios. The first ratio will be (6/10), which involves the weights of two different purchases of apples. The second ratio will be ($33/x), which involves the selling prices of the purchases of apples. Then
(6/10) = ($33/x). Solve this for x, which will be the cost of 10 lb. of apples.
You may find this solution easier if you'd rewrite this equation as (10/6)=(x/$33).