On January 1, 2016, Pistachio purchased an asset that had an estimated residual value of $700 after an economic life of four years. Pistachio used sum-of-the-years'-digits depreciation and recorded $1,560 of depreciation expense in 2018. What was the cost of the asset?

a. $5,900

b. $7,100

c. $4,500

d. $8,500