Joe started a new business this year. He had purchased a computer two years ago for $4,000 and decided to use it in his business until he could afford a new system. He could purchase a new computer with the same specifications for $1,800, but his used computer is worth only $1,100. What is his computer's basis for depreciation?

a. $1,100

b. $1,800

c. $4,000

d. The computer cannot be depreciated because it was a personal asset.