Final answer:
The equation that can be used to model the total amount Gary collects from selling computers is (D = ct).
Step-by-step explanation:
The equation that can be used to model the total amount Gary collects from selling computers is option D) (D = ct). This equation represents the total revenue (R) as the product of the unit price (c) and the quantity sold (t).
For example, if Gary sells 10 computers at a price of $800 each, the total revenue can be calculated using the equation D = ct where c = $800 and t = 10:
D = (10)(800)
D = $8,000