ECON TEST PREP QUESTION HELP ASAP!!

If a firm has 6 workers with 3 workers producing handbags and 3 workers producing phones, what is the marginal cost of producing 1 additional phone if a worker changes from handbag production to phone production?
Workers Handbags Phones
1 20 15
2 35 30
3 45 42
4 50 50
5 55 55

A) 1.25 handbags
B) .8 handbags
C) 10 handbags
D) 8 handbags