Could someone please help me with these two, it would mean a lot thanks. I am confused on how to start.

Example 2: Andrew and John are both training for a marathon. Andrew's house is located 20 km north of John's house. At 9:00 one Saturday morning, Andrew leaves his house and jogs south at 8 km/h. At the same time, John leaves his house and jogs east at 6 km/h. When are Andrew and John closest together, given that they both run for 2.5 hours?Example 3: A cylindrical chemical storage tank with a capacity of 1000 m3 is to be constructed in a ware house that is 12 m by 15 m and has a height of 11 m. The specifications call for the base to be made of sheet steel, which cost $100/m2, the top of the sheet steel, which costs $50/m2, that wall of sheet steel costing $80/m2. Determine the dimensions (radius and height) of the tank that will minimize the cost of construction