Answer
$pH=4.8$
Work Step by Step
We are given the function:
$$f(x)=\dfrac{6.5x^2-20.4x+234}{x^2+36}.\tag1$$
Graph the function $f$. We notice that $f$ is minimum for $x=6$.
Use the formula $(1)$ to determine the pH level after $x=6$ minutes:
$$f(6)=\dfrac{6.5(6^2)-20.4(6)+234}{6^2+36}=4.8.$$
