When its says $70 per car, that means you multiply 70 by the amount of cars to know how much the total car. So in your equation you would $70c and c represents the amount of cars.
You would add $50 because that's how much tips they would get. So now your equation is $70c + $50
When the first card is not replaced, you change the probability of the second card. At the very least, you have changed the total number of cards to draw from.
