Mr. wilk is a high school math teacher whose salaryis $33,660 for this school year, which has 180 days. in mr. wilk’s school district, substitute teachers are paid $85 per day. if mr. walker takes a day off without payand a substitute teacher is paid to teach his classes. how much less does the school district pay in salary by payinga substitute teacher instead of mr. wilk for this particukar day?

Mr. Wilk's salary for 180 days = $33,660
Mr. Wilk's salary for 1 day = $?
By unitary method:
             Days                            Salary
               180                           $33,660
                1                                  ?
By cross-multiplication:
1*33660/180
33660/180 = $187
Mr. Wilk's salary per day = $187
Substitute teacher's salary per day = $85
Difference in salary  = 187-85
                              =  $102
The school district pays $102 less to the substitute teacher.

Logical equivalent of the give question is its contrapositive

How many groups are there?