How do you set up linear program for this? Not asking for a solution but the objective equation and constraints

There are at least 20,000 people in Yosemite Valley that need to be evacuated by car. Each car has an average of 2.5 people. There are four highways that can be used to leave Yosemite and the rates of cars per hour are given in the table below. In addition, there are up to 100 busses that can be used. Each bus holds 25 people and takes up 2.5 car lengths on the road. Formulate a linear program that finds the minimum time to evacuate Yosemite Valley. Your solution should contain the number of cars and busses on each road and needs to determine the optimal evacuation time. While an integer number of cars is more realistic, you should assume continuous values for the number of cars. 140W Highway Cars/hour 41S 510 120E 420 120W 1000 230