YOu get this type of repeat in two major cases...
a) where the extra stitches are required to balance the knitting
b) where the pattern shifts left and right as you knit.
the first number is the basic number per repeat; the second is the additional stitches required to allow the pattern to exspress fully or balance as the case may be.
So if it says 8 stitches plus three....
and you want four repeats across your piece.
8 x 4 = 32. Add three stitches. = 35 total to work 4 repeats.