I need to create a tiered commission formula. Its supposed to read like this:

200-299 = .5 pts
300-399 = 1 pt
400-499 = 1.5 pts
500-599 = 2 pts.
600-699 = 2.5 pts.
700-799 = 3 pts.
800-899 = 3.5 pts.
900-999 = 4 pts.
1000-1099 = 4.5 pts.
1100-1199 = 5 pts.
1200+ = 10 pts.