The Torah says that Yosef gave Binyamin 300 pieces of silver. The question is why davka 300?
The Tosfos Hashalem answers that in mesches gittin(44a) it is brought down if someone sells his slave to a goy he has to pay back 10 times the value of the slave. In parshas Mishpatim it says if one’s animal kills someones slave they owe the owner 30 pieces of silver(worth of a slave is 30).We see from here that the brothers owe 300 pieces of silver (30*10),and Yosef hinted to them that this was a kenas(fine).