You're not getting 87 seats:

CAPACITY

Total Capacity: 87
Lower Deck: 22 seats (That total includes 4 priority seats and 6
preferential seats for passengers with restricted mobility) 25
standing.
Wheelchair Bays: 1
Upped Deck: 40 seats

DIMENSIONS

Length: 11.2m
Width: 2.55m
Height: 4.4m