import arcpy, glob, os
from arcpy import sa #spatial analyst

liste_a = glob.glob("folderA\*.tif") #get a list of tif (or other extension)

for image in liste_a: #loop on images
    print image # just checking...
    image_a = Raster(image) #create raster object based on the raster name
    image_b = Raster("folderB\" + os.path.split(image)[-1][:-5] + "B.tif") #idem, but adjust the name
    image_c = image_a - image-b #self explicit
    image_c.save( "folderC\" + os.path.split(image)[-1][:-5] + "C.tif") #save with new name