Can you help me with this Calculus question. First year engineering.

Lennon and Carmen shared lunch at a restaurant. Lennon leaves first, driving West at 45km/hr. 2 hrs later Carmen leaves, driving North at 35km/hr. Assume that neither of them stops driving after the latest time needed for this question.

a.) 1 hr after Carmen leaves, how fast is the distance between Lennon and Carmen changing?

b.) Consider a triangle with one corner at the starting restaurant, one corner at Lennon, and one corner at Carmen. 3 hrs after Carmen left the restaurant, how fast is the area of this triangle changing?

For purposes of both parts of this question, the curvature of the Earth can be ignored.