Rob placed in service the following property in 2020: 5-year property costing $10,000 in April and 7-year property costing $50,000 in December. No other property was placed in service during the year. Sec. 179 was not elected and Rob elected out of bonus depreciation. 2020 depreciation was:

a. $3,786

b. $4,286

c. $9,143

d. $9,643

e. None of the above

** The answer is B, just need to know how it was calculated? **