Please help (math) i just don’t understand

Use set builder notation to represent the following set: { -3, -2, -1, 0}

Acar started driving from city a to city b, distance between which is 620 miles, at a rate of 60 mph. two hours later a truck left city b and started moving towards city a at a rate of 40 mph. how many hours after the truck's departure will the two meet?

Find the unit rate for: 75% high-fiber chimp food to 25% high -protein chimp food.