Replace $T(t)$ in the equation with 59, because you want the time when the temperature is 59. What equation in $t$ do you get?

Once you have $75 - 4t = 59$, first subtract 75 from both sides, then divide both sides by the coefficient of $t$ to isolate $t$.

In Desmos, type y = 75 - 4x to graph the temperature of the liquid over time, where $x$ represents minutes and $y$ is the temperature.

On a new line, type y = 59 to graph a horizontal line representing a temperature of $59^{\bullet}\text{F}$.

Look for the point where the two lines intersect and click on it. The $x$-coordinate of this intersection is the number of minutes it takes for the liquid to reach $59^{\bullet}\text{F}$. Use that $x$-value to choose the correct answer.

The function $T(t) = 75 - 4t$ gives the temperature, in degrees Fahrenheit, of the liquid after $t$ minutes. Here, $t$ is time in minutes, and $T(t)$ is the temperature at that time.

We want to know when the temperature is $59^{\bullet}\text{F}$. That means we want to find the value of $t$ such that $T(t) = 59$.

So set the expression equal to 59:

Solve the equation step by step. First, move the 75 to the other side by subtracting 75 from both sides:

Compute $59 - 75$ to simplify the right side.

Continue simplifying:

So $t = 4$. This means the liquid reaches $59^{\bullet}\text{F}$ after 4 minutes, which corresponds to answer choice D (4).