One root of $x^2 + kx - 24 = 0$ is 4. What is the value of $k$?

Explanation

1. 01

   Put $x = 4$: $16 + 4k - 24 = 0$.

2. 02

   So $4k = 8$ and $k = 2$.

3. 03

   (The other root is $-6$, since the product of the roots is $-24$.)