How many RPM should the engine turn at 80 kph and 100 kph in a 94 Mercury Topaz?

The rpm's should be... in a standard from about 2000-3000.... and in an automatic 2500-3500. However remember that these are general estimates and depend on the size of the motor (a 4-cylinder will have higher rpm's than a V6, and so on) and the condition of the car (fluids/maintenance/etc.).