labour turn over ratio

Question
at the beginning of the year ,a company employed 4600 individuals.during the year 1800 individuals were recruited and at the of the year ,the company employed a total of 5500 individuals.
what was the labour turn over ratio?
a) 9%
b) 17%
c) 18%
d) 20%

i got the answer 35.64%. but correct answer is 18% .i don’t know how?
i calculated new employees are 2700. so replaced employees are 1800.but in answer 900 employees ars replaced.
plzzz… help …..