3. At the table, there are several boys and five girls, and on the table, on a plate, there are 30 buns. Each girl gave a bun (from the plate) to each boy she knew, and then each boy gave a bun (from the plate) to each girl he did not know. After this, it turned out that all the buns were given out. How many boys were there?
93.3. Let the number of boys be $n$. Then there are $5 n$ different boy-girl pairs. Each such pair corresponds to
one passed bun: if the boy and girl are acquainted, the bun was passed by the girl, and if they are not acquainted - by the boy. Hence $5 n=30$. Answer. $n=6$.