I have 2 questions in math that I am not quite sure about...

Question

1. Mandy begins bicycling west at 30 mph at 11 A.M. If Liz leaves from the same point 20 min. later bicycling west at 36 miles per hour, when will she catch Mandy?

2. A mixture of 10% acid and 90% water is added to 5 liters of pure acid. The final mixture is 40% water. How many liters of water are in the final mixture?

thanks:)