Suppose that k>0 and that the line with equation y=3 k x+4 k^{2} intersects the parabola with equation y=x^{2} at points P and Q, as shown. If O is the origin and the area of \triangle O P Q is 80 , then the slope of the line is
Answer Choices
A. 3
B. 4
C. \frac{15}{4}
D. 6
E. \frac{21}{4}