Norman's salary can be algebraically expressed as:
20 + 6(6) + 12(6) + 18(total - 12)
where total = the total number of bicycles sold during that week.

The first three terms in the above equation are constant. So, the only way to double Norman's income is to increase the sales.

Considering statement III, y > 3 has to be true because y > 12. That leaves us with answer options D and E.

Consider x and y as the sales of previous and current week respectively as mentioned in the question.
The variable part can be represented as

18(y - 12) > 2[18(x - 12)]
y - 12 > 2(x - 12)
y + 12 > 2x

OR y + k > 2x

Also, x and y cannot be negative. Therefore, y > 2x doesn't hold true.

That leaves us with answer D.

Moreover, if x = 18 (for example), y + 12 > 36 OR y > 24. => y > x.

Hope this helps!

Yup. thanks!