Complicated if and then function

Hello,

I work in a firm where we get paid for our work in different rates. We enter data in forms. the different rates are as follows: If less than 100 forms - 3.25/form If more than 100 but less than 120 - 3.50/form (for all forms) If more than 120 forms - 3.75/form (only the forms entered after 120 the previous forms before 120 will be charged as 3.50/form) If more than 160 forms - 4.50/form (only the forms entered after 160 will be charged as 4.50/form) its too complicated i will deeply appreciate if some tech-guru can solve this problem for us. Thanks in advance.