Answer:
Where x is the amount of dollars the item costs and y is the amount of cents. The first entry of f(x,y) is the amount of dollars to be returned and the second entry is the amount of cents to be returned.
Step-by-step explanation:
let f(x,y) be the function that computes the change.
The parameter x is the amount of dollars it costs and y is the amount of cents. both x and y should be integers and both of them should be positive or 0. Also y must be lower than 100, and x cant be bigger than d. Also if x = d, then it must happen that y ≤ c. The return value f(x,y) is a pair (a,b) where a and b satisfies the same conditions than the ordered pair (x,y) (the change cant be higher than the amount paid). a represents the amount of dollars that has to be returned and b the amount of cents.
Now, lets go to the formula. The formula should depend on wether y is higher than d or not, if that is the case, then after substracting x from d, we need to substract one more and add 100 cents to c-y (because we cant be given negative cents)