Three straight lines, l_1,l_2 and l_3, have slopes \frac12,\frac13 and \frac14, respectively. All three lines have the same y- intercept. If the sum of the x- intercepts of the three lines is 36, then the y- intercept is
Answer Choices
A. -\frac{13}{12}
B. -\frac{12}{13}
C. -4
D. 4
E. -9