In order to determine the cost of 150 dL, first convert this quantity to L, as follow:
where we have use the equivalence 1L = 10dL.
Next, if 7.65L cost $9.40, then, by using rule of three you can write:
where x is the cost of 15L. Then, by solving for x and by simplifying we obtain:
Hence, 150dL cost approximately $14.4