All hexagons have six sides, contributing 6 σ bonds.
Each C−H bond on the benzene ring adds one σ bond, for a total of 4.
The C−C bond with each methyl group counts as one σ bond, contributing a total of 2 σ bonds.
The three C−H bonds on each methyl group contribute a total of 6 more σbonds.
So, we have a total of 18 σ bonds.
Inside the benzene ring, you have delocalized π electrons over six atoms. The major resonance structure has three π bonds; one for each double bond.
So the result is 18 σ and 3 π bonds.