If f(x) is a linear function and the domain of f(x) is the set of all real numbers, which statement cannot be true?

Can somebody me out with this question

The chs baseball team was on the field and the batter popped the ball up. the equation b(t)=80t-16•16+3.5 represents the height of the ball above the ground in feet as a function of time in seconds. how long will the catcher have to get in position to catch the ball before it hits the ground? round to the nearest second

What can you determine about the solutions of this system