What would probably be the sentence for robbery and false imprisonment if the person has previos record?

There are several factors that the court considers when sentencing someone convicted of a crime. Although very heavily weighed, one's criminal record is only one of several factors. It also depends on the level of robbery that was committed, whether simple, aggravated, or especially aggravated robbery. Whoever they attorney of record is can advise on the range of punishment.

Unfortunately (or fortunately depending on the perspective), sentencing isn't that simple. It would depend on the facts of the case, exactly what the previous record consists of, whether the sentences could be run consecutively or concurrently.... The available sentences should be told to the defendant at arraignment, but an opinion on what kind of time this particular defendant may be subject to will require a more in depth analysis. You should contact an attorney to discuss.

Unfortunately (or fortunately depending on the perspective), sentencing isn't that simple. It would depend on the facts of the case, exactly what the previous record consists of, whether the sentences could be run consecutively or concurrently.... The available sentences should be told to the defendant at arraignment, but an opinion on what kind of time this particular defendant may be subject to will require a more in depth analysis. You should contact an attorney to discuss.

Prison, depending upon the facts, the charges, and the prior record, and many other factors, hardly any of which we know.

There's no magic formula. Hire a lawyer and fight for the best outcome.