How do I find the Z intercept and what is it?

1. Your weekly cost(in dollars) to manufacture x cars and y trucks is Z=C(x, y)=240000+6000x +4000y - 0.1xy a. Compute the marginal cost of manufacturing cars at a production level of 20 cars and 10 trucks. (1pt) b. Compute the marginal cost of manufacturing trucks at a production level of 20 cars and 10 trucks. (1pt) c. Find the z-intercept. What does the z-intercept tell you about cost? (2pt)