In order to solve this, we can replace 80 for x into each one of the three given functions, then we identify what value of y is the greatest, like this:
For the first function:
y = 4x
y = 4×80
y = 320
For the second function:
y = x² - 15x + 88
y = 80² - 15×80 + 88
y= 6400 - 1200 + 88
y = 5288
For the third function:
[tex]\begin{gathered} y=1.1135^{80} \\ y=5435.23 \end{gathered}[/tex]
As you can see, at x = 80 the function that has the greatest value is the third one.
