number of patients at the given weeks:
week 5: 85 patients
week 10: 65 patients
We need to select a function from the options that, for a given week "x" we get an approximate to the number of patients that they had in those weeks.
One consideration is that the number of patients is decreasing:
week 5 is 85
and week 10 is 65.
What that means is that the function we choose, should have a negative number that accompanies the variable "x" to represent this decrese in patients.
Our two valid options are:
![\begin{gathered} B\colon f\mleft(x\mright)=-20x+85 \\ D\colon f\mleft(x\mright)=-4x+106 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/l8be3mguq7sentm5c3zd06mhi0wsajw0st.png)
First we try option B. For 5 weeks x =5, and we get:
![\begin{gathered} f(5)=-20(5)+85 \\ f(5)=-100+85 \\ f(5)=-15 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/wvuljtnjr2zotn3lz0ya3b17vznsa32r55.png)
And since -15 is not even close to the number of patients on week 5, We discard this option.
Now we try option D, for week 5 (x=5), we get:
![\begin{gathered} f(5)=-4(5)+106 \\ f(5)=-20+106 \\ f(5)=86 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/sg6k3eypost14ksfg64gw6iuvo8s6ubpwp.png)
Which is really close to the number of patients on week 5.
We corroborate for week 10, x=10:
![\begin{gathered} f(10)=-4(10)+106 \\ f(10)=-40+106 \\ f(10)=66 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/6f2s4ne5sxkod9xjzifvu0m91666fb3vwo.png)
Which is also really close to the value for week 10.
Thus, our answer is:
![D\colon f\mleft(x\mright)=-4x+106](https://img.qammunity.org/2023/formulas/mathematics/college/dnxu98snyz80kbiyhwyr11zbd73u0n1lln.png)