We have two prices, $2.35 per double-spaced page and $1.85 per space-and-a-half page.
So for a report with 35 double-spaced pages adn 12 space-and-a-half pages is:
We sum the cost for each type of page, $2.35*35 is the cost for the 35 double-spaced pages, and $1.85*12 is the cost for the 12 space-and-a-half pages.