Subject: mathqa
Question: of the 150 employees at company x , 70 are full - time , and 100 have worked at company x for at least a year . there are 20 employees at company x who aren ’ t full - time and haven ’ t worked at company x for at least a year . how many full - time employees of company x have worked at the company for at least a year ?
Option: 
A: 100
B: 50
C: 40
D: 80
Answer: C