Final answer:
The function prototype for calc_total, which returns a double and accepts an integer and a double as parameters, is written as 'double calc_total(int quantity, double cost);'.
Step-by-step explanation:
The question you've asked pertains to writing a function prototype in programming. A function prototype typically consists of the return type, the function name, and the parameter list. For a function named calc_total that computes the total cost based on the quantity (an integer) and the cost of an item (a double), the prototype would look something like this in most programming languages such as C, C++, or Java:
double calc_total(int quantity, double cost);
This prototype indicates that the calc_total function will return a double and takes two parameters: the first is an integer representing the quantity, and the second is a double representing the cost of an item.