Alysa walks home from school every day. She always walks at the same speed because she wants to get some everyday exercise. It is 3 km and always takes 30 minutes. Her boyfriend Edvin intends to go and meet her. He leaves home for Alysa’s house just as Alysa starts to leave (she sends a text). He is a bit slower but his pace is 3 km in 40 minutes. How can I write the question in two equations to plot on a graph?

Need good explanation for the question!