* Engine size: Were you looking at the 1.3L, 1.5L, or 1.6L engine (or possibly a diesel variant, depending on the market)?
* Transmission: Was it a manual or automatic transmission?
* Driving conditions: City driving consumes more fuel than highway driving.
Without this information, providing a specific fuel consumption figure is impossible. You might be able to find this information in a 1983 Ford Laser brochure, owner's manual, or through online car databases that specialize in specifications.