complex DAX query

Hello 

 I have a data set containing year, week number, Number of incidents treated and Number of incidents total. There are two years 2018 & 2019.  Treated incidents is a subset of total incidents.  

A  I am wanting to calculate as a measure the % of treated sum(number treated)/ Sum(number of incident) by week number and year

B:  I then want to create a measure: the mean % of measure A  by year

C In addition using confidence.norm DAX expression I want to identify the confidence intervals for measure B 

Where I am struggling to do all this and want help with from you is to calculate the mean (B) of A. I don't seem able to do this as it does not want me to use a measure I have already created. In Area I am grouping by week and year but in B I am removing all groupings of week and only grouping by year.  Is this actually possible in Power BI?

Any help would be very gratefully received

Juliet