prealgebra question

Question

In a very long toy train, the first and last cars were blue. After each blue car (except the last one), there were two yellow cars. After each pair of yellow cars, there was a red car. After each red car, there was a blue car. Oleg picked a car and recolored all cars in front of it green. Then Joyce picked a car and recolored all cars behind it green. What is the least possible number of non-green cars in the recolored toy train if it contains 7 more yellow cars than blue cars?

Answer 1

Two yellow for every blue - except for the last.

Therefore 7 blue are need to produce 14 yellow.

So 7 times 4 or 28 is the least number of cars.