Calculate percentage in ssrs report

I have one ssrs report having matrix table which looks like this

 YEAR    A1  B1 Total percentage
 2012    23  11  34    
 2013    12  12  24
 2014    32  43  75

here i need to find percentage using below formula in ssrs expression

(Total of current year-Total of previous year)/(Total of previous year)*100

[for ex take 2012 - (Total for 2012-Total for 2011)/(Total for 2011)*100