For the conjugate of the complex number c = 2 − i.

Here are the solutions to the problems:

Question 27:
The question asks for the conjugate of the complex number $c = 2 - i$.
The conjugate of a complex number $a - bi$ is $a + bi$.
Therefore, the conjugate of $2 - i$ is $2 + i$.

The correct option is 3.

$$\boxed{\text{3}}$$

Question 28:
The question asks for the solution set of the equation $c^2 + 7c - 12 = 0$.
We use the quadratic formula $c = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$.
Here, $a=1$, $b=7$, $c