Base SAS 52

The following SAS program is submitted:
data work.total;
set work.salary(keep = department wagerate);
by department;
if first.department then payroll = 0;
payroll + wagerate;
if last.department;
run;
The SAS data set WORK.SALARY, currently ordered by DEPARTMENT, contains 100 observations for each of 5 departments.
Which one of the following represents how many observations the WORK.TOTAL data set contains?
A. 5
B. 20
C. 100
D. 500
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