Step 1: Use the condition for tangency.
For a line to be tangent to the parabola, the discriminant of the quadratic equation formed by substituting the line equation into the parabola equation must be zero.
Step 2: Conclusion.
By solving the discriminant condition, we find that \( k = -15/4 \).
Final Answer:
\[
\boxed{-\frac{15}{4}}
\]