"Thoughts and Sentiments on the Evil of Slavery" was written by Quobna Ottobah Cugoano, a slave himself, as a direct criticism to slavery and a refutal to any and all pro-slavery arguments that were being given during the epitome of the British slave trade.
On the other hand we have "Letters of the Late Ignatius Sancho, An African", written as a letter by Ignatius Sancho, also a slave, to a friend of his, Laurence Sterne. Sancho became an active critic of the way Britain handled the slave trade, but he did this through letters in the 18th century in which he mostly beseeched his good friend and writer, Sterne, to help, through his pen, to make people aware of the horrors of slavery.
In these two excerpts, although the end goal is the same, Cugoano does this by directly and fervently demanding the end of the trade, and uses the importance of the Christian faith to put forth his argument, while Sancho seeks to engage the help of someone whose words and ideas may be better heard by the public than his could ever be. This is why the correct answer is: Sancho is humbly asking for someone´s help, while Cugoano is asking for immediate and drastic changes in policies about slavery.