The Drama Club held a car wash to raise money. The equation y = 15x represents the amount of money y club members made for washing x cars. Identify the constant of proportionality.

Abag contains 5 red marbles , 6 blue marbles and 4 green marbles. susie selects a marble and returns it to the bag before selecting another marble. if susie selects a red marble 6 out of 20 times, what is the experimental probability that the next marble she selects will be a red marble ?