Seasonal variances/Trends

loopy lou

I am currently working through the study tasks in my osbourne book but can't seem to find the answer to this task. It asks for a forcast for the first three months of the next year. I have worked out the turnover the trend and seasonal variance for the first three months of this year but not sure how to work out the the same for the next year Can anyone shed some light?

SandyHood

Find the average rate of change in the trend
Then apply that rate to the future trend, extrapolate the trend, and adjust to forecast values using the seasonal variations.

loopy lou

Thank you very much