A soccer team scores an average of 11 goals per season. A double number line is drawn to figure out the average number of goals the team scores in 6 seasons. Which of the following statements is true about the diagram?

a Both number lines increase by 6.
b One number line increases by 1, and the other increases by 6.
c One number line increases by 11, and the other increases by 1.
d One number line increases by 11, and the other increases by 6.