Two cars are headed for the intersection of the two roads. If Car A is travelling south at 46 Km/h and car B is travelling East at 58 Km/h, at what rate is the distance between the cars decreasing when car A is 7 km and car B is 15 Km from the intersection?

Answer: The distance between the cars are decreasing at a rate of .... km/h (please write the answer as an exact answer not decimal approximation - for example 4/5 not 0.8))