Answer:
![f(t) = -0.05t +12](https://img.qammunity.org/2020/formulas/mathematics/high-school/hn1agwvx9xn92pu5bamnen3y269reeqfmm.png)
Explanation:
To solve this problem we must pay attention to the following data supplied:
- f It is the number of figurines that remain to be painted.
- t amount of time, in minutes, that Colin spends painting
- Colin takes 20 minutes painting each figurines.
- After painting 60 min, he still has 9 figurines left. f (60) = 9
If he takes 20 minutes painting 1, it means that in 60 minutes he has painted 3 and he has 9 left.
Then, at the beginning he has 9 +3 figurines to be painted.
![f (0) = 3 + 9\\f (0) = 12](https://img.qammunity.org/2020/formulas/mathematics/high-school/p3a1832hs58fx7kkqt6opjv95unxp8qkuo.png)
With these two points we can find the function:
If m is the slope of the line, then:
![m = (y_2-y_1)/(x_2-x_1)\\\\m = (9-12)/(60-0)\\\\m = -0.05\\\\f (t) = -0.05t + c](https://img.qammunity.org/2020/formulas/mathematics/high-school/xatv1c8gok1apvwq7nka2m93ctmugla53u.png)
Where by definition
![c = f(0) = 12](https://img.qammunity.org/2020/formulas/mathematics/high-school/mm4sb401yqqzyibleweup27n1tkic289sz.png)
Finally the formula is:
![f(t) = -0.05t +12](https://img.qammunity.org/2020/formulas/mathematics/high-school/hn1agwvx9xn92pu5bamnen3y269reeqfmm.png)