If you are going somewhere that is 60 miles away and you're going 40 miles per hour the whole time how long will it take you to get there

Velocity * time = distance

40 (miles / hour) * t (hours) = 60 (miles)

Take note how the units work. miles/hour * hours = miles. This is an indication that a formula we picked is correct.

Now, looking at our formula (and neglecting units at this point)

40t = 60
t = 60/40
t = 1.5 hours

There is 240 red cars and there is 400 blue cars because 240/3=80 and 80*5=400