I'm not really sure what to do here:

The area covered by a species of ground-cover plant has a rate of increase of ycm^2/week, given by:

y = -t^3 + 5x^2 + 6t

where t is the number of weeks after planting. According to the model, if the plant covered 100cm^2 when planted, what area will it cover after 4 weeks?

Thanks! :)