How many slaves were one horse and a length of silk worth

It would depend on the time period as in the 17th century a slave was worth around ten dollars while the value rose up to 400 dollars in the 19th century.

Explanation:

As far as trade in the Atlantic slave trade is concerned one can understand that the trade was based on practices that had little to do with barter of horses and silk.

Silk was a rarer commodity in US due to the less use of it and being made in China.

Hence, at any given time frame the value of a slave according to these would fluctuate but for a reference we can see that the value of a slave was around 10 dollars at the height of the trade in the 17th century but it eventually became more and more and reached around 400 to 800 dollars in 19th century.