look at the graph for full-time employees first. Add up the number of employees:
20+40+50=110
there are altogether 110 full-time employees, and 110 is 55% of the total number of employee
part-time employee is 45%, so 45%:x=55%:110, x=90
there are a total of 90 part-time employees
for question #27, the answer is 110-90=20, a is correct
for question #28, 60% of 90=54, d is correct.