In robbery cases they normally throw in a bunch of additional charges. Without any other information, it's challenging to give you an informed answer, but the answer in short is that the person could potentially be looking at a ton of time.
If it is a 1st degree felony, the max for the robbery charge would be 20 years. If a gun was involved, there could be a 5 year mandatory sentence invoked.
You need to get a lawyer to look into the charges.
This question cannot be adequately answered without additional information, but the max for an F-1 is 20 years.