hi there.. can someone just give me an idea to solve this problem?

Two straight roads intersect at right angles. Car A, moving on one of the roads,

approaches the intersection at 60km/h and Car B, moving on the other road,

approaches the intersection at 80km/h. At what rate is the distance between the

cars changing when A is 0.5km from the intersection and B is 0.7km from the

intersection?