at a given moment, two cars approach an intersection. car a travels south at 30 mi/hr. car b travels east at 40 mi/hr. (a) how fast is the distance between the cars decreasing at the instant when a is 15 miles from the intersection and b is 10 miles from the intersection? (b) how fast is the area of the triangle formed by the intersecting roads and the segment joining the cars changing at this instant