If Jon has r red marbles and each red marble is worth 6 points, we would write 6r as the number of points received from the red marbles.
Similarly, if Jon has b blue marbles and each blue marble is worth 2 points, we would write 2b as the number of points received from blue marbles.
Then, to find the total number of points, just add the two equations together:
6r + 2b