Find the roots of the quadratic equation x2 − 3x − 4 = 0.

We can factor the quadratic expression:

We look for two numbers that multiply to $-4$ and add to $-3$. These numbers are $-4$ and 1.

Setting each factor to zero gives the roots:

The roots are $x = -1$ and $x = 4$.

The quadratic expression $x^2 - 3x - 4$ represents a parabola that opens upwards because the coefficient of $x^2$ is positive ($1 > 0$).
For a parabola opening upwards, the expression is negative (less than zero) between its roots.
Therefore, the inequality $x^2 - 3x - 4 < 0$ is satisfied when $x$ is between $-1$ and 4.
The solution set is $-1 < x < 4$.

The solution set is $\{x \mid -1 < x < 4\}$, which corresponds to option A.

The final answer is $\text{A. } \{x \mid -1 < x < 4\}$.