the study conducted was 6 days long: there was 72mm of plant food and it decreased an equal amount each day.

Step-by-step explanation:

No. of days of study = 6

Amount of food to use for the 6 days = 72 mm

Given that equal amount of food was used each day, amount used per day =

This would enable us derive a function for the amount of food remaining f(x), which can be expressed as a function of the number of days that have passed, (x).

Thus, we would have:

Let's check if this equation expresses the relation of the function well.

At the end of day 1, if we used, 12mm, we would have 72 - 12 = 60mm of food remaining.

If we replace x in the equation we derived, we would get the same 60mm as the amount of food remaining.

If you try 2, 3, 4, 5 days, you'd get same thing.

At the end of the study, after the 6th day, the food would remain nothing.

Replace 6 for x in the relation function derived, you'd get a value of 0.

it is probably the graph on the bottom right.