6.2. The shape of a certain castle is a heptagon, and there is a bell tower at each of its vertices. Each side of the castle wall is guarded by the soldiers in the bell towers at the two endpoints of that side. How many soldiers are needed in total to ensure that each side of the wall is guarded by at least 7 soldiers?
6.2. If there are no more than 3 guards on each tower, then no wall will be guarded by 7 guards. Observe any tower with at least 4 guards. At this point, the remaining 6 towers can be divided into 3 "adjacent pairs," with each "adjacent pair" corresponding to one wall, so each "adjacent pair" has at least 7 guards. Therefore, there are at least $4 +$ $3 \times 7=25$ guards. It is easy to give an example with exactly 25 guards.