Otherwise you will get answers like this:
SELECT *, Trend = ([Week]/5.0) * MAX(Forecast) OVER(PARTITION BY [TYPE])
FROM #REport
Which exactly meets your requirements (apart from the trivial matter of rounding) but is almost certainly incorrect.
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden