Step-by-step explanation: all you have to do is start from add 1 each time you add a new line. You could do this using your fingers. Raise a finger for each line and count. Start at 5 for your first finger, and continue adding 1. Once you reach 7 fingers, you’ll have reached the number 11. This is the amount of marbles you have. You could also simply do 6+5, because you are adding 6 lines so you’ll have 6 more marbles then in the first line.
