Answer:
8 Minutes
Explanation:
since we are trying to find how many minutes have passed we first need to find how much substance was used during the time. we can do that by subtracting the leftover substance from the amount we started with.
666-562 = 104
Now that we know how much substance was used we can then use our conversion rate (13 per minute) and find how many minutes have passed by dividing.
104 / 13 = 8