What exactly did you sell? Assets? Client lists? Goodwill/workplace in force?
For assets, you will use your adjusted basis. For example, if you purchased a computer for $1000 and have depreciated $400 so far, your basis will be $600.
Your inventory will be the original purchase price.
Goodwill will be zero as you did not have any purchase price, unless you initially bought it from someone.
A business usually has many assets. When sold, these assets must be classified as capital assets, depreciable property used in the business, real property used in the business, or property held for sale to customers, such as inventory or stock in trade. The gain or loss on each asset is figured separately. The sale of capital assets results in capital gain or loss. The sale of real property or depreciable property used in the business and held longer than 1 year results in gain or loss from a section 1231 transaction. The sale of inventory results in ordinary income or loss.
The residual method must be used for any transfer of a group of assets that constitutes a trade or business and for which the buyer's basis is determined only by the amount paid for the assets.
A group of assets constitutes a trade or business if either of the following applies.
The residual method provides for the consideration to be reduced first by the cash and general deposit accounts (including checking and savings accounts but excluding certificates of deposits). The consideration remaining after this reduction must be allocated among the various business assets in a certain order. To find out more about how to make the allocation among assets in proportion, refer to Publication 544, Sales and Other Dispositions of Assets.
https://www.irs.gov/businesses/small-businesses-self-employed/sale-of-a-business