The Squirrel Population in a Region Varies Periodically Depending on the Time

Short Answer

The squirrel population in a region varies periodically depending on the time of year. If the starting population is 4,000 squirrels and the population fluctuations up and down by 1,500 squirrels on an annual cycle (more in summer and less in winter). Due to conservation and feeding efforts, the average number of squirrels increases by 100 per year. Give a model for the number of squirrels.