Well, benzene and toluene do not have the same molecular formula, since benzene is
The difference between benzene and toluene is that the latter has a mthyl group attached to the ring. That is why, according to IUPAC nomenclature, toluene is called methylbenzene, or
Toluene has 15 sigma bonds, while benzene has only 12 sigma bonds. The difference between the two comes from the fact that a sigma bond between a carbon atom and a hydrogen atom has been replaced by a sigma bond between two carbons.
One of the two is one the ring, while the other is part of the methyl group. SInce the methyl group has 3 sigma bonds of its own, the total number of sigma bonds for toluene will be 15.
You can think of this like