Questions & Answers about Visina sjedala je važna.
- visina = height
- sjedala = of the seat / of the chair seat
- je = is
- važna = important
So the whole sentence means The height of the seat is important or more naturally Seat height is important.
Because sjedala is the genitive singular form of sjedalo.
- sjedalo = seat
- visina sjedala = literally height of the seat
In Croatian, when one noun describes another like height of something, the second noun is often put in the genitive case.
Compare:
- boja auta = the color of the car
- vrata kuće = the door of the house
- visina sjedala = the height of the seat
So sjedala here does not mean plural. It is singular genitive.