Looks to me like you need to write a likelihood of the box office gross in terms of fixed reviews as predictors. You can start with something very simple like using the mean of the reviews and the std deviation of the reviews and check if you get anything useful. Since you don’t seem to have any more information about the quality (or identity) of the reviewers or the movies, there is not really much more you can do.
It will be mostly about finding a likelihood that goes reasonably well from number of reviews, and their values to box office gross
Do the reviews even predict the box office? Since you don’t have a model yet, it may be useful to do some exploratory data analysis of reviews x outcome. This can give you some ideas about the functional form and noisiness of your system.